Science fiction author John Scalzi wrote a funny little play about why publishers are necessary:
<http://whatever.scalzi.com/2010/02/03/why-in-fact-publishing-will-not-go-away-anytime-soon-a-deeply-slanted-play-in-three-acts/>
I'm not arguing for much of the publishing industry, which is full of bloated behemoths ten years behind the times, but for publishers as they could be. Some of them do get it ... like Baen. (Too bad that Baen's specialty is military science fiction, which is not exactly my cup of tea.)
The publisher is your filter. I'm a freelance editor and I am sometimes asked to serve as an acquisitions editor. I read a cookbook and opine on how it would sell and how much work it would take to clean it up. Many of the books I've critiqued are utterly wretched. I keep them from being published. YOU don't have to read the slush pile, because I do.
