The biggest differences are in the publishing and distribution of new books. In the past, publishing a book is a big undertaking. A publisher will consider the cost of acquiring rights to a book from an author, type-setting, printing and delivery of the finished books. So authors sometimes may have to sell-publish because they could not find a publisher. This is no longer the case for e-books. It can be as simple as posting a text or pdf file online to get a written book out to the public.
The largest online store, Amazon, started out as an online book seller for physical books but quickly saw the potential of e-books and has become the largest e-book distributor.
