Throughout history, Japanese marital systems had gone through many changes along with changes in Japanese social systems and conditions. The most important and historical change in the Japanese marital system was brought about through the rise of "bushi" warriors in the 13th and 14th centuries. The change from the age of aristocracy to the age of the shoguns led to a change from the old practice of “muko-iri” to the new practice of “yome-iri”. That is, instead of the groom joining the bride’s family ("muko-iri"), the bride would join the groom’s family ("yome-iri") after the birth of a child or the loss of a parent. 
It is interesting to note that a young man had more say in choosing his own bride during the age of aristocracy. A young man would typically visit the young lady of his choice at her home. If the young woman’s parents approve of their union, the young man would be invited to a ceremony termed “tokoro-arawashi" and offered "mochi" rice cakes. This ceremony was deemed to be the most important function in ancient weddings among aristocrats. 
Similarly among the common people, a young man would visit the parents of the lady and asked her parents for her hands in marriage. Labour played an essential role in life of the common people. Labour practices vary from places. In certain areas of Japan, such as the Tohoku area in the north, a groom would live with his bride's family to offer his labour for a certain length of time. While in other parts of the country such as the Izu Islands, a wife would work for the family of her husband while her husband would offer his labour to her family. It is worth noting that such labour arrangement is still being practised to this day in marriages where the man is adopted into the family of the bride upon marriage. A third and more common family labour arrangement was for the groom and the bride to offer their labour to their respective families. In such a case, the husband would visit his wife nightly to maintain their union in marriage. One word, two concepts
Needless to say that this is a personal (thus subjective) point of view, based on my experience and knowledge only, and concentrate on the most common attitude encountered in the people of each country, and exceptions are numerous.
Reason for marriage
West: Love => people promise to love each other for ever when they get married (even if it's often a dream). Modern laws make it the same to get children outside marriage, so that if people only want children, marriage is not even necessary. Marriage is usually a proof of love and commitment for life. If love disappears, people tend to divorce easily (except sometimes when there are small children, to avoid perturbing them psychologically).
Japan: Children => with or without love is not very important. Lots of marriage are still arranged ("miai") and some Japanese think that it's better than love marriage because loveless arranged marriage rarely end up in divorce as the purpose is to have and raise children, and for the woman often to quit working and care about the household. Japanese men often look down on women at work, but are usually ready to ask them to stay at home and pay for their expenses, even if their salary is tight. As the father of a child born outside marriage is not legally recognised, the marriage rate of parents is close to 100%.
Japanese family relationships
Sleeping with the child(ren) in the middle of the parents is so common in Japan that Japanese and a special name for it, a comparison it to the kanji (kawa = river). Children might sleep with their parents till the age of 3, 5, 8, 12 or even 16, depending on the family, number of children and space in the house.
Western reaction to children sleeping with parents
Westerners find for the least surprising that children sleep everyday with their parents (especially till age of 12 or later). They should not forget that on top of this it is normal in Japan for a father to have a bath with his children, even 20 year-old girls! I guess that if the average Japanese man loses interest in his wife once she becomes a mother, there is no problem with children either.
I have heard a lot that Westerners would be afraid of crushing their new-born baby by sleeping in the same bed, but I was told that it never happened (of all mammals, only male sealions and pandas sometime crush their babies to death when sleeping with them, but never humans would it seem). The good point of the mother sleeping with the baby is that the baby doesn't cry because it feels secure near its mother and has a unexhaustible warm-milk bottle at its disposal. I have read that it was better for babies to be breastfed than drink other milk. That system definitely has its advantages.
Another concern is that the parents lose their privacy and cannot have sex anymore - unless doing it in front of the child, which is a kind of taboo in the Judeo-Christian mindset. As Japanese parents stop having sex regularly after their children are born, that is not a problem.
For international couples who do continue, I was told little babies can sleep very well even with the parents doing whatever they please right beside them. But they should have their own room from age 3 or 4 then.
Finally, lots of Westerners think it might cause psychological problems to the children to sleep with their parents. But Japanese do it and seem to be alright with it. The only drawback I can think of is the independence factor. Japanese are very group-minded and usually have difficulty thinking by themselves. It may be related.
Why do Japanese women stop working when they get married or pregnant?
1. It's in the culture like that. They usually want to. Most Westerners think they are forced to quit, but they often resigned from their own will (or from what society has inculcated them). Japanese men also prefer that their wife stay at home once married. Women almost always want to spend as much time as they can with their babies (remember J-girls like what is "kawaii" ? The connection is evident).
2. Nursery schools are few and very expensive in Japan (I have heard about 200.000 yen/month). It make more sense for the mother to stay at home than work and pay almost all her salary for the nursery. In most Western countries, nurseries and kindergartens are free, which allows lots of mothers to work.
3. Paternity leaves don't exist in Japan, and (paid) maternity leave are not encouraged.
Japanese relation to sex
There is a kind a tacit understanding between spouse that after 10 years of marriage (loveless anyway) and a few children, the man is free to satisfy his libido somewhere else. That is why the sex industry is so prosperous in Japan.
Male literature in combini (convenience stores) is 90% porn and everyone reads it openly (and shamelessly) anywhere. Even serious newspapers have their "pink pages". This is just beyond belief for Westerners first visiting Japan.
Japanese men who miss talking to young and cute girls (or not so young and not so cute, depending on the price and place) go to hostess bars or "snack" after work. Nothing much happens there except dirty talk. Those who want to go more carnal have the soaplands and massage parlours, but Asian men's testosterone level is reputedly lower than Caucasian or African men, so they are often satisfied with just talking, watching - and groping...
There is also the infamous "enjo kosai" or teenage prostitution. I'd like to say that for lots of Japanese (or East Asian) women, this isn't even considered as prostitution. Many find it normal to have sex with a man that pays them whatever they want. Remember that marriage is not much more than a man giving almost all his salary to a woman to make children and take care of them. It surely sounds utterly shocking to lots of you, but after talking to (female) Japanese and other Asian friends I know quite well, they don't even see it as abnormal. It's in the mores, that's all. That does not mean Japanese women cheat more, but lots of them certainly consider money as more important than love or sex (which I find very saddening).
Behind this, I have realised that cuteness (the kawaii factor) is very powerful in Japanese women's mentality. They like babies, cute anime characters and cute clothes more than anything else, it seems. Men have an obsessive care about their job and status. My impression is that this stereotype works as well for Korea and China, if not also South-East Asia.
Divorce and charge of the children
In 95% of cases in Japan, the woman gets the exclusive charge of the children. It only seems natural as the father often don't really care about them. He comes back late from work and rarely take part in their education. After a divorce, it's not normal for the father to just forget about his offsprings. He doesn't care very much. That's the mother's role to care for them.
That might sound crude again to some Westerners, as in the West parents sometimes fight bitterly over the charge of their children, and in peaceful cases, it's usual to find arrangement such as the children stay one week with the mother, next week with the father, or, weekdays at the mother's and weekends at the father's. Anyway, lots of fathers would feel terrible not to see their children regularly (see the thread about children abduction in this regard).
Here in Japan the following are advised:
A. a marriage registration form (konin todoke) from the consulate.
B. marriage certificate from the country in which you married.
C. Japanese translation of this marriage certificate with the translator's name and seal or signature on the document.
D. copy of the Japanese spouse's family register (koseki tohon).
E. a valid passport
