(Assuming Pa. is Obama’s and Fla. is Romney’s)
Romney needs Ohio, that’s it, plain and simple, there’s no way he can win without it.
However, Obama can lose Ohio as long as he win N.H. and Virgina or N.H. and Colorado or Virginia and Colorado. And in that last scenario, if Obama wins Colorado and Virginia and loses N.H. and Ohio he can even lose Iowa to Romney and still win.
Point is, Obama’s got a lot more ways to win.