Anecdotal evidence alert!!
I seem to recall every football season in my addled memory beginning with the following statement (or a variation thereof):
The defending national champ is #1 until somebody beats them.
Not arguing the point one way or the other...just throwing logs on the conflagration.
Whoever said that may staunchly believe it, and it may be one way of doing it for
preseason polls, but currently the polls (both preseason and regular season) have not embraced that motto, nor should they in my opinion. UT was #2 in 1999, FL St. was #2 in 2000, OK was #3 in 2001, etc. In fact, of the 13 BCS champions, only 4 started out ranked #1 in the preseason polls for the season after their championships.
Granted, none started as low as #23. But, as mentioned previously, I'd dare say that Auburn lost more talent and was left with more younger, inexperienced players than these other national champions. That's a complete guess, but given the other teams' abilities to blow out their opening day opponents (aside from LSU in 2004), it would appear on its face to be true.