As much as the hardcore world record holder LFSers are going to hate me saying this, there's no doubting the fact that a computer sim is a very different ball game to driving the real thing.
Whilst undoubtably many of them would be fast in a real car, it doesn't mean they'd be anywhere near the speed of any pro race driver even if they could beat them on LFS. The whole lack of reset button makes a big difference when driving for real, and a lot of people find it hard to put the whole "if I crash now, am I going to die" thought out of their heads.
Furthermore, there's no 'seat of the pants' feel in a game and also, it's only 2D. A lot of the reference points I use when I'm racing for real don't exist in a game. One of my strong points is feeling the grip ebbing away when it's wet or on long sweepers, which just can't be done on a PC. The best way I can describe it is (ironically) that driving a real car fast is very anologue, as opposed to a sim which is very digital (as in every braking point, turn in point, and acceleration point is exact and can be rehearsed time after time). As you say, it's therefore possible to get really fast, just by playing the thing for hundreds of hours.
Once again, I'm not taking anything away from the skill of sim racing, but a 14 yr old behind a desk is not really comparable to a 21 yr old in a 200mph missile!