I think there's two things. As you say, it has to be an elite defense, not just very good, but also, it's no way to win consistently. You can put together a great year, maybe two, with a defense and run the ball mentality, but that's about it. This is what I was most annoyed with Urlacher's statements earlier this year. He laments that they aren't a run the ball and win with defense team anymore, saying that it worked with Orton. The problem, of course, is it didn't work with Orton and they are no longer a very good defense, let alone elite. That was about a 1.5 year window closed abrubtly.