I believe the pistons do move....when brake rotors warp you feel it in the brake pedal and steering wheel. The calipers take some of it but so do the pistons....to much going on there to not.Those are some interesting pictures, LawrenceS. It does support the transfer of pad material to the rotors.
I'm still trying to figure out how warped rotors supposedly cause the brake pedal to pulse. Warped rotors would still be the same thickness everywhere. The entire caliper would potentially move, sliding on the pins, but the piston wouldn't move.
To answer earlier posts, when you turn discs and the meat of the rotor is off getting disc that have different thicknesses around the disc, it's bad casting. I see that with cheap foreign made rotors. Quality control issues for sure.