Also England and half of Australia (although it's 'passing on the left' that's illegal because cars drive on the left there.) I used to think it was a silly law but now realise that it's not actually about passing on one side being safer, but about creating social pressure to force slow drivers out of the fast lane (since they can't just expect people to go around them.)
It makes sense to be a lot more strict about it in locales where vehicles are allowed to operate at widely divergent speeds on the same set of lanes. In the US many major roads have both a maximum and minimum speed limit that's within 30mph and most folks are actually driving within 10mph of each other.