A JFK Jr. underling pens a memoir. As an author you would want a story to go on as many computers, Web sites and devices as possible. They'd prefer to leave the business of promoting a book and getting it to readers to a publisher. Publishers are printers and foot the marketing bill. The other problem for authors is distribution.
Publishers know how to distribute books.
As many have observed, if King wanted to get into the business, he could certainly afford to buy his own publishing house. I think we will be having a very different and interesting conversation about this issue in three years. I think a lot is going to change. And traditional publishers have taken note as well. If anything, they will seek to expand their dominion through this new medium.