Well the problem is that even though it is easy to say the QB crossed the first down marker, it was completely impossible to see where the ball was at the time or if he even had it. The whole point of the replay is to get the correct call and to overturn a call on the field they must have indisputable video evidence which is something they did not have on that call. Without being able to see the ball it is not only reasonable, but rather easy to dispute the overturn.
By them overturning the call on VERY disputable video they completely threw the whole point of the replays out the window and just did as they pleased. They also did it at a time that had a major affect in the outcome of the game.
Now should one questionable call get them suspended no, but factor in that it removed one of the conferences most popular teams from bowl eligibility and the possible revenues that were just lost and I could see the conference using that as a reason to suspend them.