Carrol Smith is a well know and respected driver in the racing industry. He passed away in 2003, however much of his written knowledge is still applied today. His most popular book is Tune to Win, with other versions such as Drive to Win and Engineer to Win. I briefly skimmed over the article, and I don't believe he is saying rotors are never uneven and there is no need for rotors to be turned down, but the reason for the increase tolerance in the rotors is not the rotors itself being "warped", but the friction pad material not being applied evenly to the rotor for a few reasons, causing a pulsating pedal, or the term "warped rotors". It seems like what some people will call a warped rotor, he considers uneven deposition, but doesn't consider the original cast rotor as "warped".
"In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures."
http://www.carrollsmith.com
