Absolutely true! a 30fps racing game is not a high end racing game. That's simply a fact. In fact, with Forza 2 the physics rate is 360 times per second. This means your car may be traveling less than foot each increment when physics is calculated, rather than traveling about 5 feet (at 60fps), or about 10 feet at 30 fps. Do you really think your car's physics should be updated every 10 feet?
My calculations were done at 200mph, but if you change it to 100mph then you can divide the distances by 2. You can see that 60 calculations per second is the bare minimum, even if you don't mind getting 30fps (and a hardcore race fan will mind).
Then again, if you want fast times in GT5:P, you have to bounce off of the walls. That's already proven.