One of the smallest costs in the price of a book is the amount paid to the author, sadly. A lot of it is overhead which doesn't magically go away just because there is no physical media.
That said, one of the big problems is that selfsame overhead. Is it necessary? Most people would say no. So far, we have not had an eReader publisher, specifically created to serve a no-physical-media market. It will come. Will it be successful? Hmmmm. Bezos got a lot of flack for trying to create a non B&M bookstore. We see how that turned out.
Mind you, it's revealing that there is still only one, and it looks like Amazon isn't going release that crown any time soon.