All civilization was just an effort to impress the opposite sex...
This is what I get for reading too much while my physical prowess is slowly being restored: a head full of cross-cultural ideas and a blog on which to vent them.
Many people have posed theories as to why paleness was and still is an admirable trait among women in Japan. For that answer, I'd suggest looking to David M. Buss, psychology professor at my alma mater and author of The Evolution of Desire: Strategies for Human Mating. That's right, kids: everything comes down to impressing the opposite sex, as I think Futurama sums up quite nicely in that little public service announcement.
"The most culturally variable standard of beauty seems to be in the preference for a slim versus plump body build. This variation is linked with the social status that body build conveys. In cultures where food is scarce, such as among the Bushmen of Australia, plumpness signals wealth, health, and adequate nutrition during development. In cultures where food is relatively abundant, such as the United States and many western European countries, the relationship between plumpness and status is reversed, and the rich distinguish themselves through thinness. Men apparently do not have an evolved preference for a particular amount of body fat per se. Rather, they have an evolved preference for whatever features are linked with status, which vary in predictable ways from culture to culture. Clearly such a preference does not require conscious calculation or awareness." - The Evolution of Desire, David M. Buss
Precisely. As much as we'd like to believe we are completely independent of social norms and not slaves to conformity (yes, even in the Japanese "group mentality" mindset), you can't exactly fight hundreds of years of cultural evolution overnight. Just as paleness in western cultures was once associated with high status (e.g. duchesses and princesses who were "kept" - their beauty or lack thereof restricted to castles or places of riches out of the sunlight), so the US and many cultures have reversed this standard based on the image those in status present.
No longer are the rich usually locked in golden prisons far from the sun-weathered skin of peasants, but rather they are adventurers, out in the sun and using their wealth to live to the fullest (well, most anyway, even if it is just lying on an expensive beach). Who knows who started the change to bronzed goddesses rather than the pale ones atop Olympus?
Yet, in Japan, this cultural landmark simply didn't happen. Oh, of course, you'll see some Japanese laying out on the sand trying to achieve a picture-perfect Hollywood tan just as others anywhere in the world would, but by and far paleness is still a trait associated with high status and being financially secure, at least in terms the opposite sex intuitively understands.
I can only speculate as to why this particular aspect of mating behavior has been prevalent for so long in Japan...
1. This country retained so much of its cultural identity at the expense of shutting others out for a long time. There were influences from the Catholic church, the Portuguese, the Dutch, even a little from the British, but for the most part, Nippon was closed off to the rest of the world until the end of the 19th century. As a result, Japanese had little-to-no reference as to what those across the globe considered associated with prosperity and wealth.
2. The old rather incendiary argument that Japanese women are more prone to conform to a man's needs, rather than his to hers. By this logic, women would want to have pale skin not primarily to appear successful and attract a mate, but to raise the status of her current mate in the public spotlight (i.e. that man is with a pale, attractive woman, therefore he must be special).
3. Geisha. This argument is quite like the "chicken and the egg", but merits a mention, as there were and still are geisha in Japan (incidentally, the first foreign geisha started work not too long ago - Sayuki of Akasaka). Sentiments of the geisha profession aside, I doubt anyone has associated one of them (highest of those in the "floating world") with low status. And what do they do? Accentuate their features, especially by painting the face white.
4. Stricter adhesion to gender roles. It is a brave new world now, but as recently as fifty years ago, the Japanese (and the US, western cultures, of course) had a more predominantly patriarchal society: women stay at home, in closed doors, raise the kids; men go out and be bread-winners. Anyone who showed physical signs of straying from this "divine plan" (sun-weathered skin, for example) would be considered a social deviant - not necessarily out of reach, but requiring more effort than most, and as such, less desirable.
For some, being a Japanese woman simply means falling into the outdated "one race, one people" idea that all Japanese are monoethnic and immutable: a Japanese women is pale and short, and has black hair. To change this precept would be to deny the culture and heritage of being a Japanese.