I definitely don't think it will be released at WWDC. Other than that, I'm not sure. I still have a year to go on my contract so I'm not going to worry about the iPhone 5 until then, so I don't mind to see a bit of a delay
Stock does run low though, so they could be just allowing merchandise to move through before ordering more. To me, having some kind of deal or something that would suggest AT&T trying to dump the iPhone 4 would be a greater indication of the 5 coming out... but alas, I don't know anything