In addition, there's some strange geographic variation--Obama's winning by seven points in the Cincinnati area, but losing by a full 30 points in the Columbus area (this despite the fact that Cincinnati has only marginally more African-Americans than Columbus, and actually has more senior citizens too). In Cleveland and Dayton it's effectively tied, while Clinton's way ahead in Toledo and rural southeastern Ohio. Perhaps commenters with more knowledge of Ohio political demography than I have might shed some light on what's going on.
The best explanation for this is that Cincinnati has traditionally been a very Republican area, probably the most Republican large city in the U.S. (Bush actually won Hamilton County in 2004). To the extent that Obama does better among dissenting Republicans and independents, he's probably more likely to find them in greater numbers in the Cincinnati area.