I know there probably are some folks who can tell, but it would be very interesting to do a blind taste test and see who really can of those that say they can tell, including myself.
That is probably because it is easier to get HH on charcoal than it is on most gas cookers. If you cooked two identical steaks side-by-side at exactly the same temperature, one on gas, and one on charcoal, my guess is that the crust would be identical.