When you factor in coaching changes (head coach, coordinators, position coaches), key players not playing due to declaring for draft, inconsistent match ups, some teams having "home field" bowl locations, and extra time to prepare it all adds up to very different results than the regular season.

The playoffs obviously have much higher stakes so those are valid to look at. But the other bowls have too much variability to be used as a concrete measure for comparison, IMHO.