Recently, it was confirmed that Universal Studios is about to make a major announcement concerning the upcoming mini theme park, "The Wizarding World of Harry Potter" on September 15th. This is appearantly true, for Universal began sending out press invitations. Much speculation is surrounding this announcement, for Universal and Warner Bros have kept things very quiet up until now. One possible explanation could have something to due to this fact. As construction began for the HP addition to Universal's theme park, it was stated by officals from both companies that the HP addition to the Universal park would debut somewhere between Fall 2009 and Spring 2010. It is possible that Universal has chosen a premire date, and has decided the time is ripe to announce the exact date.
As no confirmation has been announced concerning this, this possibility should be counted as a rumor until either company confirms it.