According to the TOS, messages posted to GH are the property of GH.
Now, the way I look at this, is that while the content of the message belongs to the user, the message and the space it occupies on the board belongs to the board, and in a way, to the community.
The user is free to remove his or her personal information from the account, that's entirely possible and not an issue. The non-personal information (the post contents) are by definition not personal information, and are not protected under any sort of personal information protection law. It is now community content, and removing it from the community would cause damage to the community, and there's no real reason to have the information removed in the first place.
If he's truly concerned about the privacy aspect of it, all the information can be removed from his profile without much trouble. He can even do it himself -- profiles are freely editable. He can then throw in a random string as his new password, and essentially brick the account to stop anyone else posting in his name. However, I feel that's rather excessive.
Despite this, it has been politely requested and politely denied, so I don't see why we're still arguing about it. Possibly because we've had some people being somewhat less than polite at this point? In any case, unless someone specifically addresses me again, I'm washing my hands of this thread. It's a job for the admin team.