A typical schedule for a playoff contender is roughly 4 solid opponents, 4 OK opponents, and 4 pastries (which really cannot possibly win), plus ostensibly a CG against another solid opponent. Out of the solids, you may find 1 really really good opponent (a PSU, ND type). The 4 pastries don't count and the 4 OK opponents don't really count either unless you lose to a Syracuse, and then obviously it hurts, but perhaps at times those losses get excused more than a loss like OSU had versus OU.
It's weird to me that Penn State goes on the road to a hostile environment and loses by one point in a great comeback and drops as far as it did. If one pass happens to be dropped late, PSU is still #2, not #7 or whatever. In effect, PSU is almost out of the playoff, and they could very well have a top four team (IMHO).
For the Wisconsins and Miamis of the world, they have played some OK opponents and pastries, but have not played a solid opponent to date. They are for me akin to a Houston or Memphis at 8-0 at this point.
A playoff team can afford a close loss to a half decent opponent or solid opponent if they are 12-1, but that second loss is simply too much to traverse for most teams who rarely will have 2-3 impressive wins over very very good teams to compensate. That second loss is too much for compensation unless you happen to have beaten 2 or 3 really good teams, and you rarely have that chance (Iowa State).