Charles Stross's blog yesterday was illuminating on the subject:
Anyway: this is why I don't self-publish. Yes, I could do it. But it'd suck up a huge amount of time I would prefer to spend doing what I enjoy (writing) and force me to do stuff I do not enjoy (reading contracts, accounting, managing other people). The only sane way to do it would be to hire someone else to do all the boring crap on my behalf. And do you know what we call people who do that? We call them publishers.