Lots of ifs here, but in consideration of those who point out that USC did win certain games on the field, and therefore should retain honors, awards, or titles for such games, the thinking goes as follows:
First, we must assume that USC knew or should have known of Bush's indiscretions. With that rather large if out of the way, we are then left with a situation where other schools knew or should have known, or properly monitored, their own athletes' behaviors. For schools who did monitor and suspend/prevent such activity, they played shorthanded. USC, by in this hypothetical having not properly monitored their athletes, would then have had an unfair advantage. We could, finally, not know how the season should have ended up based on what was played on the field, as certain teams were handicapped and USC was not. So USC did receive, in this scenario, an "unfair" advantage.
What if Tressel, but nobody else, knew of Troy Smith's "issue," and then told nobody let him play and practice as a starter pre-2005? Would he have beat Texas? Been better for Penn State? Would OSU have won the MNC? Afterwards, would it be fair to say that it was a righteous win because it was played on the field?
To make the analogy more correct, what if nobody found out about Troy's booster $ until after the 2005 season, and OSU did win the MNC, and OSU did fail to monitor properly? We all saw what happened in reality, and what then would have happened had the monitoring been sufficient. . .
Just a hypothetical about USC, but it is certainly not so simple as to say that everything was decided on the field anyway. . .