What shock me in this avegrage salary is that they work at Monolith Soft, making games that generates millions of $. I earn more than that (particularly because of the ) in a shitty web agency in Paris. I do think being a 3D artist for Nintendo games is way more valuable.
This is truly a game of telephone. The OP states it as the "absolute minimum" and a few dozen posts later it's become the "average salary".
Anyway, it comes as no surprise. Video game salaries are known to be rather low in Japan. It's the not the kind of industry you want to work in if you don't love what you are doing.