Printing+ distribution+shipping entail a significant percentage of the cost of publishing a book, so I'm not sure about that. Even if thats the case, digital downloads should at the very least still be cheaper, even if not by a lot. They ARE saving money and significant logistical overhead by skipping the entire process. And unlike movies/music/videogames/any other media, bandwidth costs are basically non-existant, and file sizes are ridiculously small. Whatever is being said, it's only logical thats its costing everyone less money.
Books are bigger then music files, by a several meg. To say bandwidth cost are non-existent is not true...