Publishers do provide editorial service. If an author writes a book in a year, there're more than 2 years of editorial process before the initial writing becomes a consumable.

Books aren't like software where you can release often and iterate. Think about your weekend prototype project. And how much effort it takes to make it into a "successful" start up. For books, you put all the effort before printing. And that effort to turn a prototype into a profitable product is what publishers provide you. And many publishers are really good at that.

Of course with ebooks and tablet, you can start thinking of a book as software: an interactive multimedia thingy that can be updated often. You are welcome to innovate this digital medium. But we are not there yet.