Cracking is considered normal, but don't let the cracks get too big. Ask around at the track next time you're there, ask your service manager at the dealer, and ask a good independent Porsche mechanic. You'll get some different advice on when to change the rotors once the cracks start but the dealer won't call it a part failure or warranty item, of course (translation, its normal wear).

 

I had almost the same unusual "no pad contact" areas around the outer circumference of my 997S front rotors right after I bought the car (used). I checked and confirmed that OEM pads were installed, so I decided to just replace the pads. When I removed the pads, I found them quite crumbled around the outer edges. The center part of the pads looked fine, and the rotors were fine. My assumption was that the P.O. had tracked the car and overcooked the pads.

Upon installing new OEM pads, the rotors were once again "wiped" through their entire radius. Maybe this is common with the OEM pads?