[canvia]

Perhaps there are other correlating factors such as obesity that tie into these disparities: http://www.cdc.gov/nchs/data/databriefs/db131.htm

[runako]

It's almost not worth addressing, but read your source carefully and note that the disparity isn't enormous. Most Americans skew toward obese.

[yummyfajitas]

It's absolutely worth addressing. But the answer is that OK Cupid's data controlled for attractiveness.