I'll give a real answer, I guess.
Perfect timing, perfect coach, plus 7 additional years of experience.
Saban had undoubtedly learned some things in the 7 years between taking the LSU job and taking the 'Bama job that he wanted to do differently.
He was also the perfect coach for 'Bama. He is a defensive guy who likes to run the ball. He has a no nonsense attitude and tells it like it is. He's not satisfied with anything less than perfection. That wouldn't work at USC, but it works perfect at Bama.
And it was perfect timing. In 2008, Alabama had one of its best crops of HS talent in a long time. Julio Jones, Marcel Dareus, BJ Scott, Tyler Love, Mark Barron, Jerrell Harris, Robert Lester, Courtney Upshaw, Michael Williams, and Brad Smelley were all part of that class and from Alabama.
We already had guys like Eryk Anders, Rashad Johnson, Javier Arenas... I mean, those guys were hardly even recruited... and combined them with that crazy 2008 class. I know we like to think that the rest of the SEC was "Sabanized" but they weren't. They were just exposed. Tuberville, Fulmer, Houston Nutt... the SEC West just wasn't very strong then. Florida and Georgia were the big dogs. So we got to win the West pretty quickly.
I think that immediate success began a cycle - recruits were amazed by how quickly Saban turned us around and were much more easily convinced to come to Tuscaloosa. They were immediately convinced that Saban was building a giant.
So our recruiting just went off the charts. Our talent level has been so high the last several years that they have allowed our rocky seasons to be 10-3, 11-2 type seasons. As good as Saban's recruiting at LSU was, his recruiting at Bama has been even better. And I think it's just a cycle - the better we do, the better we get at recruiting. The better we get at recruiting, the better we do.
Just pontificating.