So I do have some thoughts on this subject after all.
There are sales to be made, I think, along the “would you like to have fries with that?” model. You just bought a comic book. The digital edition has some extra pages of some sort (more comics pages maybe, or an interview with the creators, or early sketches and thumbnails — something). Some people would agree to tack on an extra fifty cents for a supplement to the print comic they’re already paying for. While this wasn’t the focus of the Diamond announcement, there was some of that thinking in there (particularly when they were talking about the Rick Geary graphic novel in the interview at The Beat). That sounds like a good digital business for a retail comics shop to be in.