It is simply a fact — a fact — that a lone author can distribute 100% as effectively by herself as she can with the assistance of a multi-billion dollar international conglomerate (again, editing, marketing and all the rest is a separate story; for the moment, we are talking only about distribution).
To put it another way: a publisher offering an author digital distribution services is like someone offering me air. I already have it and I don’t need to pay extra for it. I know it can be unsettling in some circles to have the matter stated so baldly, but I really don’t think the matter is disputable, either. In digital, as Clay Shirky has said, “Publishing is a button.”