On the 10th anniversary of Baldur's Gate, Bioware put up a website that had quotes from a bunch of devs who worked on it. One of the people quoted said that the publisher, Interplay, kept rejecting Bioware's story drafts and ended up having their own team (Black Isle) write it. So if that is to be believed, Interplay/Black Isle did do more than just publish the game, but I haven't been able to find out exactly how involved they were in the development.