Driving License

I'm studying about New Zealand Road Code because I intend to tanslate from Japanese Driving License to New Zealand's.

If you have a foreign driving license, it can translate to NZ Driving License. It's very good system, I thnk, but there is a 'not understandable' rule. If you have the U.S. driving license, you can translate automatically, it means that you don't have to take an exam about NZ Road Code. But If you have the Japanese license, you have to take exams: about Road Code and driving test. In NZ, however, you have to drive a car the right side of roads. In Japan, also you drive the right side but in the U.S., you have to drive the opposit side. Why Japanese have to take exams and American don't? I can't understand!?

Anyway, after I get the license, I want to go to Maruia Springs. There is spas. I like a spa very much. But there is another problem. I don't have a car!