I also heard it was because Joss feels like he's "respecting" the studio by agreeing with the final film they put out...like he feels he;s going against them if he did a directors cut. I don't know something like that. It's why he won't apparently do one but I mean when you've cut an hour worth of footage just put it back in...I mean apparently some of the stuff would explain the pool of water Thor gets in to go back to his "vision" as that wasn't very explained.

I feel a longer cut would make the film even better