I don't think it's people braking to hard (or at least not all of them). I also have a lot of brake dust on mine and I'm a pretty laid back driver, I don't ride the brakes or stop at the last second.
The first time I took mine in for warped rotors the guy accused me of riding the brakes because of the ammount of brake dust. I've since taken it in a second time for warped rotors and now its almost time for it again.
I guess I should just get the aftermarket Powerstop rotors and maybe I woln't have a problem with them warping as much.
Richard