Does any one else use your car and "ride the brakes" or do you drive on twisty mountainous roads?
The rear brake pads should normally out last the front pads two to one. I wonder if the rear brakes are working properly. If the rear brakes were not functioning correctly the front brakes would be doing more work and generating more heat causing the rotors to warp. Could the front calipers be "dragging"? Are the brake pads wearing prematurely?