There's also the issue of "does the username belong to the user". So if user a deletes their comment and user b quotes them both by comment and name, should user a's name be masked when they delete said post? Well, isn't that user b's content that's now being infringed upon? The current non-delete mode is fine - just don't write stuff you don't want on the web on a forum, and if you do then update with a new comment retracting the statement.