It's one thing for Boise or TCU to beat a team like Va Tech at the beginning of the season, or Auburn in a one-off NC game after facing very light conference competition.
Their players have to be healthier, plain and simple, than a team from a major conference that takes beatings every week. As is commonly said, in football there's a difference between "hurt" and "injured." By the end of the year, almost everyone is "hurt." But those same players play unless they're "injured." It seems that with conference schedules like Boise's or TCU's, there's necessarily a lot less "hurt" AND "injured."
Moreover, if it's "body of work," as we constantly hear from NCAA eval committees, how can Boise's or TCU's bodies of work compare with, e.g., Auburn, etc...? IMHE (and it is, indeed, a humble one), they can't.