Is this because the yen is worth too much, boosting Japan's GDP per capita at market exchange rates? The yen has indeed been appreciating quite a lot against the dollar since 1980. Or is it because goods are too expensive in Japan, reducing people's purchasing power? Maybe goods are too expensive because Japan is too protectionist, not allowing cheap Chinese goods to flow in. Or maybe its goods are of higher quality, something PPP exchange rates capture rather imperfectly.
So here's what's weird. When the Japanese travel to the US, there are much richer than the Koreans. But back home, they both live as comfortably. Do they really?