FWIW, don't overlook the rivlary games Ohio State and Oregon have to play this weekend. Washington and Michigan, while not having great seasons, still have the players to beat their rivals. Oregon has a bit of a little brother complex to Washington. They'll never admit it, but Washington has a more reliably good program than Oregon, for a much longer history (or at least that's my impression having grown up in the Pac-10).
These are exactly the kinds of games that make these rivalries great: one team is on the cusp of greatness, the other is having an off year, but brings all it has to this game. I don't have any statistics on it, but I'd bet that the winning percentage for the higher ranked team isn't much different when the lower ranked team is a 2-loss team vs. a 4-loss team (I know, Michigan and Washington are both 5-loss teams, but the 12-game schedule is still relatively new, for the purposes of historical CFB statistics).
Wisconsin won its first Rose Bowl as the result of Michigan winning one of these kinds of games. I'm sure there are many other similar examples.
The favorites are playing at home, which will help even more, but don't sleep on the challengers.
