That's because of its manual gearbox.
It's been the subject of much debate lately whether or not future sports cars should be offered with a manual gearbox. With a dual-clutch unit's ability to help deliver even greater performance numbers, automakers like Porsche really don't see the need for drivers to row their own gears any longer. And that's an absolute shame because cars like the 997 911 GT3 are all about driver engagement. But that's where Porsche sees a weakness, because humans make mistakes that a dual-clutch won't.
Sometimes those mistakes are intentional simply for the sake of, say, exploiting that torque curve for all its worth. On the other hand, that can interfere with the car's performance and Porsche doesn't like that. So is the old 911 GT3 the last great purest Porsche? Sadly, it's quite possible.