Im with nisskid, because you are a good driver on LFS, it doesn't mean you're a good driver in RL, in RL, you have fear, and if you damage your car, it costs, you can't simply Shift+P and get it fixed, or if you crash, you can't Shift+P and everything's fine, and away you go. In RL, you crash, chances are, at least, it hurts, and you constantly have this in your mind (be it at the back of, or front of), whereas in LFS, at all times, whether you try to make it feel as though its RL, you are constantly aware that if you crash, woopdidoo, Shift+P, s'all good.
One point I would like to make however, is that LFS definately increases understanding of physics, and how the forces affect the car, however, you don't see how the physics affect the driver, and so, how you'd react to the different maneuvers.