The rotors warping have nothing to due with the brakes being worn out.
If you feel it at all in the steering wheel that it is the fronts. If you feel it more in the seat it is the rears. The rears have to be really bad for you to feel them so more often than not its usually the fronts that are causing the pulsation.
Improper wheel torque, improper installation, debris between the rotor and hub, hot spots, and rust spots across the rotors surface can all contribute to a rotor warping.