I think you are confusing "warping" with deposits on the rotor themselves. That shutter is not caused by the rotors being bent. What happens is the rotors get deposits from the pads (especially aftermarket pads) which are not deposited evenly and causes the pads to grip differently on one side or even one part of the rotor resulting in a warping feeling. Decent rotors especially BMW factory rotors don't usually warp.

Sometimes this is cleared up with a series of hard stops to redistribute the pad materials more evenly on the rotors. If you remember, there is a process where new pads on new rotors need to go through what they call a bedding process. That is where the materials are embedded into the rotors and if done incorrectly will result is jerky braking.

Just a thought,

Michael