Two of the three most popular MMOs in Japan are Korean. It is well known that Koreans are wild and crazy for their MMOs, regardless of how many exist. US based MMOs don't even put a dent on the chart which is incredible when you think about how popular they are here in the states.

Ragnarok Online, Sukatto Golf, and Final Fantasy XI lead the pack in Japan. RO and Sukatto Golf are Korean while FFXI is a domestic fan favorite. The retention rates of players is astronomically high and is the reason why these games are so popular. Ragnarok Online boasts a 27% retention, meaning 27% of the people who have ever played it, still play it today. FFXI and Sukatto Golf show 58% and 56%, respectively.

Sukatto Golf is still under development for the Nintendo Revolution and should prove to be a hit when it comes out. Developing for the Revolution will allow them to get an even larger audience which should bring in the precious revenue.

The reason behind the popularity might be the fact that these games are cheaper in Japan, which means more people can afford them and continue to play them, regardless of their graphical capabilities.