Then you end up with a lot of debate over who's #4 and who's #5. And if, God forbid, the #4 team should win it all you end up with crying from the #5 (who thinks they're just as good) and the #1 (who doesn't think the #4 belongs in the first place). Take last year. Did #4 Texas really belong in a playoff with USC, Auburn, and OU? Did #5 Cal deserve to be in it less than Texas? Especially with Mack Brown's stumping for votes, you'd have a lot of pissed off Bears.
Besides, if you have a playoff, you end up with a lot of debate about home field advantage. Say Texas ends up #1 and UCLA #4 and the first round is scheduled to be at the Rose Bowl. Is that fair for Texas? And do you guys really think fans will want to travel hundreds or thousands of miles for multiple rounds of a playoff? The director of the Orange Bowl is gonna be pissed as when he ends up with two teams from across the country playing in a semifinal game (or even a quarterfinal with an 8 team playoff) in his bowl. You really think that many people will travel cross-country for an early round playoff game?
Take the bowls out of the playoffs entirely, and all of a sudden bowls mean nothing. The NCAA will never let that happen. I don't see a playoff coming any time soon. Talk about it all you want, it's not happening. And I'd rather have the old system than this crap.