Crisis is good for the president
None of the states hammered where going to go for Romney anyway, so whatever reduction in the overall vote happened didn't change the electoral vote. It did, however, give Obama a chance to look very presidential and people tend to line up behind the president during a crisis.
Heck, since Republicans tend to more of followers then Democrats, you could make the case that more are going to be inclined to vote for a Democrat in a crisis then Democrats who would be inclined to vote for a Republican president during a crisis.
It also helped that Obama and FEMA did a much better job then the disaster that happened after Katrina. Looking presidential is nice, actually being presidential is even better.
Jay