I would say games are probably where Japan has most excelled in software, at least in the 80s and 90s. But the code is probably very bad practice by modern standards (hand coded assembly hacks, all game state in global variables). When you only have a few KB of RAM/ROM there is a lot less scope to mess up (although I have come across bugs in cartridge games myself).
The console frameworks and API's are all produced in an SDK that other developers use .. so its just as valid an example of a successful Japanese software product.
