While Japan certainly has the technology and bandwidth for the service it is very difficult to move large business into Japan. Netflix is a North American service and the copy right laws have been dealt with in these countries. Moving to another country would require all new copy right laws, and moving through a bunch of red tape.
This is a tough one to answer, and one that would probably be answered in the Netflix blog if there is a chance of it happening soon. Currently they are working on getting in on the South American Market, so even though there are no plans on moving into an Asian market currently, it doesn’t mean they never will.