If I were to write a book, either technical or a novel, I would be tempted to hire a freelance copyrighter, editor and publicist, then list it on Amazon, Safari etc. myself.

You can find these people on Elance and similar sites, but there is an opportunity for a website that is a one-stop-shop to do all of this in one place (ie. find the various people, organize listing, sales etc.).

Anybody know if this already exists?

I can't see them disappearing completely, possibly they will become more streamlined where the author can get a better deal only taking on board services they need.