I have been pulled over for precisely that, artbrooks. In Oklahoma, for instance. And it is relevant. redhorse (presumably from the UK) said, "In US it's perfectly legal to overtake on the inside on motorways (please correct me if I'm wrong) which can catch a UK driver by surprise."

Clearly it's dangerous for people to not know which side it is customary for people to pass on. If it is customary for people in the UK to pass on the outside, operating on that assumption in a country where the opposite is true could create dangerous situations for them. Why you would discourage anyone from informing them of this difference in the way things are done, and thereby possibly saving them some trouble, is beyond me.