First, here's a bit from the 4e D&D GSL:
Notwithstanding the foregoing, except as otherwise provided in this License no Licensed Product (as defined below) will have a first on-sale date prior to October 1, 2008.
The added emphasis is mine.
Now, go here and scroll down to where it says "GenCon Releases (In Stores Early September)".
Yeah, interesting, huh?