Well, I never bought into the myth, that Japan is or becomes irrelevant for gaming. It isn't. PC and Xbox isn't doing too hot there, but for everything else Japan is the biggest or second-biggest market. I personally also think (and thought back then) that launching the PS4 later in Japan was wrong and hurting Sony.
and yet USA is 4 times as important as Japan for Sony and Europe (with a similar taste in gaming) is 5 times as important as Japan for Sony.
18.6% of PS1 sales came from Japan
14.7% of PS2 sales came from Japan
12% of PS3 sales came from Japan
8.3% of PS4 sales come from Japan
Japan IS getting more irrelevant each year. Though that doesn't mean that it is irrelevant at the moment,