The point is that the betting line would be influenced by bettors who favored their team, say ND, in numbers sufficient to render the line unbalanced vs "reality". I'm sure the Vegas boys understand this and set initial lines accordingly, if it's real. Let's take ND-USC, MAYBE they know ND gets a preference with bettors, so the line would have been say -5, but they set it at -6 by understand that ND bettors over play their team. Then when the excess bets come in on ND to win, they don't have to readjust much.
My point is not how Vegas judges real lines, but how bettors on certain teams MAY over populate betting on their team.
I do still think one can do OK betting the underdog in bowl games.