They spent so much time translating it because they didn't want to be accused misinterpreting it. Apparently, they had four sets of translators to make sure they got it as correct as possible.
Also, they were wary of giving bin Laden any more airtime on American airwaves.
Another thing, bin Laden is relaxed and happy in the video. The gov't was wary of broadcasting this pleasant image of Osama to Osama's supporters and sending the false signal that Osama is okay. It's obvious that since the video was shot, Osama has had to run and probably isn't feeling so smug.