In due respect to those who are discussing the question here, and their opinions and such, I don't think I should get involved, really, but the emotion to say something overwhelmed me at the moment--maybe cause it's morning, the sun is out, the coffee tastes especially good...whatever.....
I feel the OP question could have been worded much more precisely, but with titles, perhaps that is just the way it goes. I will share my feelings and perceptions regarding my personal history, in hopes that it may in some way provide a sample space from which others can provide theirs, and then we may be able to get a bit of some kind of picture. [and I do this all the while keeping Damacci's situation in mind. . . please understand my Tucson friend]
From birth, I am convienced, I had a propensity towards a certain type of look in women, which blossomed in highschool. As it turned out, that look was found more so in the build that comes most ususally in Asian women. (and I'm including some range of Indian here, as well as native American)
It is true, though perhaps it had not been so pronounced at the time, and I had not really been mature enough to have done so, that I vowed to myself around the age of 14 to never marry an American woman. I believe that meant to me at that time, the European based look more than anything else.
(I did have some American girlfriends after that but none so steady)
I was with a girl from Pakistan for a short while when in college, then Japanese. The reason for being with the Japanese girl was the physical attraction creating the impulse to form the connection, the building of friendship and a 'mating' parnership then, in turn, led to it being steady. [I mean, this is most usually how we sexes come together in bond anyway] It failed.
The girl I am with now was, as is so often used here, my type--very close to the girl who had been in my mind for so many years that I can remember. Alas, I am speaking of physical build, form, and activity--that includes posture (an important factor in the attraction element for me).
None of the other ideas presented in earlier posts, fit my case. I would not attempt to deny that some of those other ideas are present in the real world out there, but would neither say that they are the bulk of the 'why' matter in relationships that are between a female of Japanese nationality and genetics and a male of some (usually) Western nationality.
Some good posts have been made, I have enjoyed the read. I'll try to find some topic relatively soon too...if I can....