To me it wasn't really a surprise -- and it shouldn't have been considered an upset, either. It was obvious to me that OSU was flat-out better than Oregon, and I used their most recent games leading up to the championship games to gauge them.
Sure, Oregon beat Florida State handily. But FSU was by far the most overrated team in the postseason this season. Of the four playoff teams, FSU was the one who really didn't belong (though there was no way they'd miss the playoffs, with an undefeated record). They won some very close games against teams that weren't all that exceptional, and they probably would have lost a playoff game against any of the top 10-12 NCAA teams this year. Oregon really didn't prove anything to me by beating them.
Ohio State, on the other hand, simply looked more and more dominant as the weeks went by. They went into the Big Ten championship game against Wisconsin as the underdog ... and they won that game by a score of 59-0. I don't think I've ever seen anything like that happen before.
Obviously the selection committee weighted very heavily the late-season play. It's been said that in college football it is often more important how you finish the season than how you start, and this is an example.
The Wisconsin game was one of total domination and if you look at the stats and some of the replays you will see that. Everything clicked, passing, running, defense, special teams, whatever. You might see that kind of performance once in every hundred games you played, and done with a QB who had never started a game before for the team. It was obvious this was a team that was peaking at the end of the season and those are the kind of teams you want to see in playoffs and bowl games.