So your telling me that if Spiderman, LOTR had opened up in June it wouldn't have done great? I don't think so!
Everybody seems to be forgetting that Hulk is an internationally recognized icon like Spiderman or Superman. You can't go anywhere on this planet, where they either have a television set, or sell comic books, and show someone a picture of Hulk and they not know who is is. The fact of the matter is that because of the leaked work print, like you mentioned before, people got the heads-up of the horror that Universal had concocted.
From the premier of the teaser that aired with Spidey 1, people were hyped for this movie. The trailer, with Banner stearing in the mirror, then Hulking out, was awesome..and people couldn't wait for it to come out. It was when the superbowl trailer aired, that **** started heading downhill. I don't know exactly what it was, but people got the hunch that this movie was not gonna be great. I don't fully understand it myself. The CGi was not that bad in the trailer, i've seen worse, but peoples instincts started taking over..and well, you see how it turned out by the lackluster B.O.