Amazon and friends do have something to offer: eyeballs, and their good name. So they can negotiate.
I think you'll see newbies entering through what used to be called "vanity publishing" via Lulu etc, getting picked as a rising talent by reviewers, getting in the press, and finally being offered a contract by Amazon. This latter will become the equivalent of the old status of "published author".
Even so a system something like this would be a win-win situation for authors, distributors and readers (and more arguably for the environment in terms of reduced need to chop down trees and transport books around). The distributor could also supply additional services at a cost, such as the ability for readers to have their private libraries in "the cloud" as a dropbox type of system. So I think the distributor would have sufficient scope to add value around the product that an author may not have much incentive to leave prematurely.