Russell Grandinetti, an Amazon’s executive (NYT 10/16/2011):

...the landscape was in some ways changing for the first time since Gutenberg invented the modern book nearly 600 years ago. “The only really necessary people in the publishing process now are the writer and reader,” he said. “Everyone who stands between those two has both risk and opportunity.”

It's more like early newspapers, rather than books. For example, Benjamin Franklin successfully published and edited his own newspaper where he wrote too, under multiple pen names. It worked in a relatively small town, but when newspapers wanted to expand their circulations they created large publishing houses.