The web is great at cutting out the middleman. That's what Amazon was going to do with ebooks. Apparently their plan was to fix ebook prices across the board, then start going behind publishers' backs and appealing to authors directly. There's still a middleman in that equation, though: Amazon itself.
When the retail chain goes from author to publisher to retailer to customer, the author has to do very little for themselves except write. If they're selling directly to a retailer, they'll have to take over some of those functions themselves, like editing, proofreading and some advertising. Cut out the retailer (which is possible with the web) and authors also have to start managing sales, delivery and everything else. Although 100% of the sale price would be going straight to the author, some people would prefer to let others handle the non-writing part of the business.
Mokalus of Borg
PS - My guess is the more you want to do those things yourself, the more you're writing for the money.
PPS - But since I'm only ever at the customer end of the chain, I'm not well-informed.