Quote Originally Posted by Alhanelem View Post
For the same reason you stated, It wouldn't be fair to the japanese for those servers to be moved elsewhere as their lag would increase, and everyone else is already used to the original setup. It makes no sense for them to move the old servers.
That is why you wouldn't move ALL the "old" servers to a different region and leave some in Japan. Giving the option of "old" server to "old" server transfers for "old" players at launch (which I'm pretty sure they said will be possible), they give everyone the option of choosing which server fits their needs the best.