The yanks rarely install roundabouts, but where they do the priorities are arranged for the vehicles approaching the roundabout to have priority over those already on the roundabout (!). They don't seem to grasp how essential it is for vehicles already on the roundabout to have priority over those approaching, European style.
Actually, I believe it is only essential that all users of a roundabout agree on the same rules of priority. Beyond that, I agree that the European style is sensible and preferable.