You've heard whiffs of it already--okay, more than whiffs if you're watching Fox: If not for the economic crisis, McCain would have stood a pretty good chance to win.
The problem with this isn't so much that it's wrong (I think it is, but don't have the patience to rebut it tonight). It's that it's idiotic. It's not like the economic crisis resulted in voters' brains being reprogrammed to force them to vote for Democrats. The reason Obama benefited from the economic crisis is that voters trust Democrats on economics more than Republicans, and they especially trusted Obama more than McCain. This is not some arbitrary development.
Arguing that McCain would have won if not for the economic crisis is, in effect, like arguing that McCain would have won if the election weren't about the issue people care most about--if it were instead a referendum on, say, earmarks for research on bear DNA. Again, maybe literally true. But not much of an excuse.