lived in Japan for 3 years and saw many men (including myself) come down with "yellow fever". I have a few theories on why white guys go gaga for asian girls:
1) asians are thinner. I have only seen a handful of full-on Japanese "chubs". Even fewer in places like Thailand and China.
2) asian women are more domestic. If they are first generation, they will likely cook and clean. I know guys who find japanese roomates, not to look at or for sex, but because the dishes stay washed. American women, while cleaner than american men, are slobs by comparison.
3) asian women do more to look nice/fashion. NY is a bit different, but compared to the midwest, asians win hands down in spending money to look pretty.
4) asian women are exotic. Having sex with an american girl after a stint in asia feels like sleeping with your sister. Just too much familiarity, both psychologically, and physically.
I would also like to add, that American women are just as guilty of similar behaviour. I can't count how many times I've seen a white chick go gaga for a "romantic and charming european" or guy with a "scottish accent". These guys are the same slobs as back in the states, just dressed up nicer and maybe from a culture with good food. It's all marketing.
that being said, I now have warnings for the asian fetish white guys:
1) not only are they more traditional as in "I'll do the dishes and ironing honey", but also as in, "I obey whatever my parents say"
2) they might seem docile and sweet at first, but they get pissed off just as badly, and often worse than their western counterparts. They can bring nagging to true art form. Most guys don't even realise how bad it is, because they have more subtle control, and they are blinded by the whole "dude, I'm dating an asian chick" thing.
3) they are flat! Flat chest, flat ass, flat face, flat hair. NOTHING is bouncy and jubilant on an asian girl. (unless she's philipina, but that's cause of the spanish blood)
4) it's all fun and games until you're married with two kids. Asian women make the ugliest older women of any race.