Over the years, it has come out that traditional publishers do thousands of dollars of work on every book they publish, work that their authors don't do and don't pay for. Self-publishers can, indeed, do this work themselves, and they do. But not only do they have to fund all the work themselves, paying for professional level editing, cover illustrations, design, and marketing, they also have to learn everything that needs to be done.
A case in point--printing.
Andrew Watson's Book Printing 101: What You Need To Know Before Approaching A Printer appeared at Jane Friedman's Blog. I don't mind admitting, I was shaken by all the details involved.
Now, I suspect there are companies out there, Amazon might be one of them, where self-publishing authors can just press a few keys, and everything will be taken care of for them. But isn't somebody, somewhere, still making decisions about types of paper for the text and types of paper for the covers, and what types of hard covers, and on and on?
I have probably said something similar to this here before, but it's worth saying again: You just can't exaggerate what self-publishers need to know to give their books a chance at being successful.