I also don't think biased officiating is the same as "fixed". I think it is entirely possible, probable in fact, that refs get intimidated by the champions.
Probably the most visible case in point was Muhammad Ali. In his later years, diminished physically, he'd fight to try and be upright at the end. Then he'd get the decision. The quote was coined, and is still used today "you've got to knock out the champ!". In other words, you aren't going to get the calls when you are playing the defending champion. It isn't that way in basketball (Jordan Rules), Hockey or baseball. In fact, there are videos of umpires calling strikes for Greg Maddux before the ball crossed the plate. And we see how tOSU and UM games are called.