krambman
I think that there are probably two things that helped contribute to this being overturned.
1. West Virginia reporting the same practice limits violations under RichRod.
2. The fact that the NCAA ruled that Michigan was only violating the limits by a small amount, not the 10+ hours a week extra that they were initially accused of.
Since he did the same thing at West Virginia one could argue that he didn't know the rule or that he wasn't aware he was breaking it. Had he only done this at Michigan it appears that he knew the rule and chose to break it. Also, even though all of those who spoke out at the beginning had independent and consistent stories about exceeding the limits by hours per week the NCAA only found them guilty of violating it by something like 15 minutes a day. Had the NCAA found them guilty of violating the limits to the extent they had been accused I don't think this gets overturned. I also think that the fact that this was his first violation and it's a relatively minor violation that it didn't warrant him being accused of a failing to promote an atmosphere of compliance.