Originally Posted By: The Critic
Rotor replacement is dictated by the minimum thickness, amount of runout measured, surface condition and amount of disc thickness variation.
Not sure about his Audi, but on most BMWs the rotor material is so thin that it won't last through two sets of pads, and you don't want to be replacing rotors half way through the life of your pads, so that's why BMW recommends to have the rotors replaced at the same time as the pads.