Jack Sparrow only becomes cursed after he "accepts" a position on the Black Pearl and takes the gold-- so clever. By being cast off the ship, Bootstrap may have been "fired" in a rather spectacular way, before the curse had made itself known, and thus was no longer part of the Black Pearl's crew and no longer part of the curse.

I'm thinking that Barbossa never expelled nor released any of the rest of the crew, leaving them cursed as he was.