Yeah, I forgot about that one. Darth went from being a name to a title. Just like Sith (Dark Lord of the Sith) went from being a Jedi that has become a Sith to a race of people. Of course, that's more of an EU thing, but it's a change nonetheless. It took hime 20 years to change Darth though and that's probably only because he couldn't think of a name for the bad guy.

Someone once told me "Star Wars is a constantly evolving story". My response was "Then GL needs to say that instead of telling us that it was always meant to be that way".