Its not completely a myth though. People can get brand new cars every year for the slightest disability - how is that reasonable? Why does everyone on disability have to have a new car? What's wrong with a decent one?
I know a guy, who has been on the sick since the early 80's with 'tennis elbow'. Every year since 1988 (at least) he has had a new 'people carrier' type car. Why he needs this is anyones guess but he does because he can, probably edged on by the dealership. Of course, this doesn't mean the scheme should be scrapped, many people benefit from such a scheme. But if we're struggling for cash in the NHS, then a clampdown on pee takers is a reasonable start.
But if he is getting a new car then there's a good to high chance he's losing out on benefit elsewhere (obviously there's a debate about whether he should be getting benefit at all or at what level).