I'd be surprised to see audio books included in the hardcover, as there are extra expenses involved in producing them (voice talent, sound engineering, etc.) but the rest sounds great.
I'm a big believer in paying for the content license, rather than having that inseparably bundled with the format. This reminds me of how software sales have gone lately, where you can download for one price or pay extra for a CDROM and/or box and/or printed documentation. As displays get better and more portable, I think we're going to start to see a lot of this for books.
Regarding hardcover vs. paperback production costs, don't forget the binding. Stitching signatures of pages together is more expensive than gluing a stack of pages into the spine, and lasts longer, too. But not everyone wants to pay for it, which is why we have paperbacks in the first place.