I'm guessing there are different clients.
(Before my post gets deleted again from moderators thinking I'm breaking NDA) There was a tweet on the GW2 twitter page of someone asking if they needed to download a new client for the pre-purchase betas. The answer was that anyone who was involved in previous betas before the pre-purchase events will need to download the client they sent in the pre-purchase beta e-mails. So one would assume there is also a release version client. But then again, I don't know.