The way I see it, SEC fans are like that kid we all knew in elementary school that had like 12 favorite teams, so that at any given time, he could always brag that one of his teams was winning. The average Auburn fan, for example, realizes that Auburn has only been to one BCS bowl. Therefore, he becomes an SEC fan so that he can still puff out his chest if the SEC representative(s) to the BCS win their games.
That's one theory. The other theory is that by promoting the SEC as the toughest conference, the typical SEC fan has an excuse for why his team didn't, once again, make it to the NC game and has 5 losses, namely because his team plays in the toughest conference. If the SEC does well, the SEC fan thinks he can make the ridiculous claim that even though his team has 5 conference losses, that team would go undefeated in what he perceives to be one of the lesser conferences.