Our cars are equipped with a "limited-slip" rear differential and electronic wheel spin control. This means that the amount of wheel spin is controlled but not eliminated. Therefore, the right rear wheel will see exaggerated wear when driven aggressively without full blown burnouts. So, IMHO the wear is normal but preventable. The easiest cure is a proper rotation pattern evey oil change. (The more aggressive the driver, the more frequent the rotation should be.)
The harder cure is to alter the driver. ( I Rotate every 2500 miles or so) :cool
You may also want to get a four wheel alignment of the car. Not sure if your wear is even across the tire or just one edge. If the wear is not even across the tire I would suspect the independent rear suspension is not properly aligned. One of the car magazines noted in their test of the GTO that theirs required two hourse in a frame shop to solve rear alignment problems from the factory.