Nintendo made the Wii Wheel to help Mario Kart become a "bridge game" - to get all those new Wii Sports gamers to try something with a bit more depth. The game was built from the ground up with the "bridge game" vision in mind.
The PS3 market is pretty different. The people purchasing GT5 are going to be familiar with racing games, and the developers are not trying to appeal to anyone aside from past GT owners.