But I never said it was the "primary" factor. If I implied that, then I apologize. Certainly, the team's overall ability is far and away the most significant factor in determining home field advantage.
However, certain teams always seem to outperform at home, and I just cited Wisconsin as an example of that. If Wisconsin can be that dominant at home with a lesser (though still talented) team, then Michigan should OWN the Big House. As I perceive it, at least some part of the difference is the in-game atmosphere -- Camp Randall consistently trumps the Big House in that regard.