Check out this article:
Maybe it isn't rotors but rather pads with insufficient temp capacity?
I thought I'd ruined a set of rotors recently, upon tracking my 500 at The Glen running only Euro-spec front MBZ pads. Left a LOT of pad material on the rotors, and the sensation of warped rotors upon braking was shockingly severe. I swapped over to a set of Axxis Ultimate pads, and in about 500mi. of street driving my brakes are (finally) back to normal. Never would have believed it!