I don't disagree, but I don't think the playoffs should necessarily include all the teams that "could" win a playoff game. You do that, you start minimizing what is the greatest regular season in all of sports. Alabama "could" probably win a playoff game every single year, but they still have to play their way in via the regular season, and that's a good thing.
I'm not saying an 8-team playoff would be a bad idea, but when I'm watching these games I don't really look at the teams that were #5-8 in the rankings (Wisconsin, Auburn, Ohio State, and USC) and think it's too bad those teams didn't get a chance. I don't think Wisconsin or USC would beat any of these teams if both had a 3 weeks to prepare and Auburn and Ohio State kind of had their chances to make a statement earlier this year and crapped the bed. That's the way it goes. Basically, I think even with just an 8-team playoff there'd be a pretty high risk that a couple of those 1st round matchups wouldn't be all that compelling in a lot of years. I think the system in place, while not perfect, isn't bad.