Your rotors and pads also heat up when you stop too... I think it takes a great deal of heat to warp them (or theyre under turned)
I wouldnt think that theyll warp the rotors if you put the parking brake on, unless you allready waped them from stomping on the brakes hard. When the rotors's moving, and the static pads touch it, thats when heat (and stopping power) are created... If theyre hot enough to warp the rotor AFTER you put the parking brake on, youve got bigger problems
heres a parking paw assembly (tks howstuffworks)
http://auto.howstuffworks.com/automatic-transmission12.htm
I guess its not really a gear with holes, but more like a specially cut gear, with notces for the paw
~Nate