The OKCupid research doesn't account for socioeconomic backgrounds, which is ridiculous. Marriages are essentially financial transactions with significant economic considerations. Most people date within their socioeconomic background. This is much likely a greater bias than racial bias. Blacks are underrepresented in higher economic classes which are dominated by whites - not hard to see why dating between both races would be affected as a result.

It's also likely the case that the OkCupid research samples heavily from the US population. Interracial dating in the US is encumbered by massive historical baggage from the slavery era. For instance, black women in the US are the only group of women that I'm aware of that are more inclined to "marry down" than to "marry out".

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

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

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