I dunno but it must be different on PC. Imo the physics are really good on the PS2. Are you talking about car control or collisions or both? I feel the difference between cars, big rear wheel drive cars push you into spins, then you have the nippy little front wheel drive cars along with big brutal 4X4s that don't really turn!
Theres always total carnage while racing, with cars bouncing around you, being tailwhipped into flips and off the track! When you rip up things like fences, it causes a some power loss and loss of control whereas bigger objects can cause you to totally lose it.