Western culture is the biggest culture in the world, i think white people are considered attractive because of this influence more than the scientific theories.
if you don't get what i mean, i'm meaning how western culture is often viewed as wealthy, glamorous, healthy, fun, etc, all those things that people get a false identity of being cool, right and most of all, attractive.
My thoughts anyway.
EDIT: I don't think the majority of people commenting on this post actually understand what you are asking, you are asking this on a cultural perspective am i right? so people stop with the silly answers of "beauty is within" its not what the question is and not the right strand of answer.