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The game released in Japan about five years before the US, so we've been catching up on content for a while. In 2009, they started releasing content adding some Asian ports into the game, with ports in Japan, Korea, Taiwan, and China. They added them in a different order for different language versions of the game, so each country got its own ports first.
So when it came time to add them to the American version of the game, what do they add first? America, of course, even though that hadn't previously been in any Asian version of the game. Apparently the American update went live in Korea at the same time, and possibly some other places.
No word on when we'll be getting the eastern Asian ports in the American version. I'd hope that's next on the agenda. Trying to maintain a code base with different content added in different orders has to be a nightmare.