Here's my attempt at an explanation:
Most European race tracks are raced in a clockwise direction, and on most of those the pit lane is on the inside of the track; so when the driver comes in to make a pit stop, he is on the right side (literally) of the car without getting in the way of oncoming traffic.
That's the scientific explanation.
The one that makes more sense to me is that post-war motor racing basically originated from Britain, and most sportscars, and later puropse built racecars, came from there as well. So I guess the world just stuck with the RHD for racing puropses. The gear change is on the right side of the driver in most racecars anyway so it probably isn't so difficult for drivers from "LHD countries" to adjust.
Does it make much of a difference, though; as the example of the R8 shows, LHD isn't a handicap at all
