Rotors warp but most people won't get rotors hot enough to warp them.
I personally believe that warping/pulsating brakes that most people encounter is due to simple rotor exposure to water. Notice every time you walk to your car after its rained (and has been parked), its already rusted. However, behind the pads where it stayed dry there is no rust. After a few hundred/thousand cycles of this you will end up with high/low spots due to the fact that the rust if removed the first time you brake.
I got this theory from a brake guy I worked with at Honda, and it makes sense. Ever since I have garaged my cars every night i have never had warped rotors. My civic has 85k miles and the brakes are straight as can be.