Dean, rotor *wear* is expected. Premature *cracking* is not. Remember that set of rotors that came off your car w/ cracks all over the place? Remember the EBC greens you were running that caused those cracks? Remember me telling you "I told you so"?
Granted the Greens did a terrific job of stopping the car. But they put the hurt on the rotors to the tune of 1 set of rotors per set of pads. Maybe not a big deal on stock WRX rotors, since they're cheap, but running those on my StopTechs would turn those $100 pads into $400 pads. Meanwhile on my Ultimates/R4 shedule, I've gone through 2+ sets of Ultimates and 3+ sets of R4's and I'm just now thinking about replacing the friction rings.