The human hip, Serenity. The argument is that moving just the foot is more accurate than pivoting off the hip. It's an interesting observation which in a vacuum you might consider valid, since getting linear input out of your typical pedals is impossible without moving the hip. I don't see the point, because I don't see how moving the hips leads to inaccuracy? It's been the method since airplanes were invented after all.
You have to agree that the VKB pedals look cool even still.