Two reasons I can think of. Chinese government having a love/hate relationship with the west might be tempted to plump for Open Source systems which they might be tempted to write themselves, not good for MS, the other reason is that with a more visible presence in Chinese Republic they can help the government keep and eye on the those naughty O/S pirates, anyway it's always good to be on the inside, keep your friends close and all the X-Files guff!