I'm not even a USC fan and most of what you've typed is hearsay. The NCAA has actual proof of Tressel's cover-up, while no hard evidence exists regarding involvement on the part of Pete Carroll or any other member of his staff with regards to Bush.
Bush acted as an individual as far as the evidence shows. And yet, USC was slapped with a "lack of institutional control" charge. For what? One player taking shitloads of cash and gifts on his own volition?
Again, it doesn't add up.
School A gets a two-year postseason ban, a 30 scholarship reduction, and a national championship rescinded. School A had one player, who was the face of college football at the time, take a ton of money and gifts.
School B gets a one-year postseason ban, a 9 scholarship reduction, and a Sugar Bowl win rescinded. School B had 5+ players, who weren't the face of college football, take a decent amount of money and gifts.
Again, I think it all boils down to the fact that the NCAA was far more embarrassed when Bush turned out to be a cheat because of how much they invested in his image.