In the '80s and '90s Japan made most of the games cause of the video game crash in USA. The last ten years however America has made a comeback and are making at least as much games as before and yes USA and Japan is the two most important markets for developers. Japanese made games however usually sells better in Japan, and American games sell better in USA. I think Japanese games is still doing good in the world though, with some genre exceptions. But they are not dominant anymore like they were in the NES era.
