An author that I like has had a new book out recently. Audible sent me an email to suggest it to me, but I thought that I would rather read it than listen to it. I couldn't find it as a book anywhere and it turns out that he has only released it as an audio book.
As far as I can tell (three chapters in) there's no reason that it couldn't also be a regular book/ebook, it's not in play form and there is a single narrator (him who was Merlin, he has a lovely voice). I'm enjoying it in audio form, but I'm not sure how I feel about having the choice of format made for me.