Interestingly enough from what I read, GW2 is labelled as either: the best game to ever be devised, created, beta tested and will be the only MMO worth playing upon it's release or; it is big on idea short on execution.
June 28th is only 5.5 weeks away or so, it's not a particularly long period of time. Maybe they want to get in ahead of MoP for WoW though as that seems to be heading for a US summer release.
Edit: a lot of release dates of late have been leaked by various sources so it wouldn't really surprise me if it was a real release date. *shrug*