I can imagine after driving these mountain roads. They're not even wide enough for kei's, let alone full sized cars. I think the Japanese navi are fine though, it's just Google isn't as sophisticated in Japan.

Funny story, when I first came to Japan I was with my friend and his girlfriend. My friend decided to let his girlfriend drive his mom's car and she turned down a road that became so narrow it ripped the side mirror off and scratched the shit out of the car. Lesson learned I guess, if it looks too narrow, don't go down it.