1) It would decimate some of the late season rivalry games. Remember the 2006 OSU vs. Michigan? 1 vs. 2? That would have been a tournament seeding game and would have meant nothing. The reason OSU vs. Mich. is a better rivalry than any other is because the stakes are almost always high.
2) Are fans going to travel to up to three bowl games, with two of them on less than one weeks notice? As it is now, fans have a month to finalize their plans to the bowl game. But, as good as OSU's fans are, can they travel 45,000 three times to different sites around the country? And, if you make the first round game a home game you eliminate on of the BCS bowls, which will never happen.
3) Look back through the BCS champs, how many can you dispute? How often does the NCAA Hoops tourney crown the BEST team?
4) In 2002, OSU and Miami were the CLEAR #1 and #2. No one else even deserved a sniff of the title game. But, with a playoff, you would have had four two loss teams competing for a national title. This isn't basketball were there are ebbs and flows during the season. CFB has a finality to it that no other sport does. When OSU lost to USC in September, they were eliminated. That was it. In 2002, no other team deserved a shot.