I'm too lazy to investigate this so I'll just say this as hear-say:
The naming rights to bowl games have been sold out as far as 2035.
If this is indeed true, would it be breach of contract to go to a playoff system and re-assign the naming rights to each playoff game? Would there be enough playoff games to cover everyone (I'm looking at you whoever motor-city bowl)?
I firmly believe this is the major reason for not going to a playoff system.
If I owned the naming rights to a major bowl, I would certainly consider restructuring the naming-rights contract to fit a playoff scheme, because I think it would bring in more viewers (based solely on personal opinion). I don't consider most bowls right now to be appointment viewing, but I certainly would consider each playoff game to be such. I think a playoff system is better for business all around, not mention it would be AWESOME!
Perhaps to get around the naming rights issue you can still have crap games like the motor-city bowl played on a Wednesday between playoff games or something. Nobody watches those POS bowls unless their team is involved or its played locally anyway.
Without thinking about it too much I'd like to see conference champions and say 2 wildcards based on BCS rankings (to cover teams like Alabama this year) make it, with byes given to the appropriate teams. Is that enough to stop teams from getting snubbed? No, but it's vastly better than what there is now.