Technology is having a profound impact on the process of publishing. It used to be that the only option for self-publishing a book was to hire a printer, publish however many books you thought you could sell, and then cart them around to bookstores and try to get the store owners to put your book on their shelves. It took a fair amount of money and a huge amount of effort.
A new option for self-publishing printed books these days is print-on-demand or POD. A POD machine such as the Espresso can crank out a single book almost like a photocopier cranks out a report. The book can be digitally printed, bound, and and trimmed in about 15 minutes. Once these machines get more affordable, we might even see them in bookstores. But for now, most POD services operate with both the production process (where the author provides the book content) and the sale to the reader happening online. Some examples are Lulu and Amazon's CreateSpace.
This means that POD doesn't provide any noticeable advantage when it comes to getting a book into a bookstore. Also, the books cannot be produced as cheaply one at a time, so they can't be priced as competitively as ebooks.
Which is why I went with publishing my books as ebooks only, rather than also adding a print option. I haven't totally written of the idea of producing print books, but making the book look decent takes some skills I don't have.