Flexor the Mighty!
18/100 Strength!
Buisness history is littered with firms that "couldn't possibly loose all that market share" and then proceded to do so. Not that I'm saying that would happen with D&D but you can't assume that they are invincible. Based on what I've seen of how WOTC runs the D&D brand with surveys and market studies and whatnot I can only assume that they kept levels due to thier place in D&D success and the way they help make it easy for new blood to pick up the game and make a character. I don't find toolkit games to be nearly as easy to get going in for new people. Not that I don't like GURPS and other games like that, but I'm a 20 year gamer.