ALOT of Obama's fanbase, if you will, comprises of college students and young people. Voters age 18-30 usually only have a 17% voter turnout. You may claim that this is the year the youth vote matters, but look what happened in 2004. I kind of suspect that as the school year starts up again, absentee ballot applications are going to get lost and deadlines are going to be missed and the youth vote turn out isn't going to be significantly higher than it has been.
McCain's voter base? Older people. Who always vote. ALWAYS.

But of course this isn't a feasible explanation and everyone is racist!!!