Well, when I asked the question, the only thing that I really wondered about was whether or not self-published books had contributed to the academic/popular history paradox Hess notes. But if you're asking me if I believe self-published books are inferior to those put out by traditional presses, I hadn't thought much about it; I don't believe I can give a blanket yes or no answer. There are some really good ones out there. Daniel Masters', No Greater Glory: The 144th Ohio Volunteer Infantry in the Civil War, (Lulu, 2010) is particularly good. But there are some real stinkers out there, too.
Whether a book is good or bad depends upon several things: subject matter, interpretation/bias, the author's writing ability (and background), the thoroughness of the research, the analysis, and the argument, to name a few. Some books are strictly narratives - regimental histories, for example - and that's fine. Books that contain references and a bibliography are the most useful, but not all of them include those.
In terms of their physical layout, I have seen nothing wrong with the print quality, layout, or binding from any of the publishers, although sometimes photo reproduction lacks crispness.
But, regardless of quality, the goodness with self-published books is that they include subjects that traditional presses often ignore. And that's not always a bad thing.
Two final observations. There was a time was when the term for self-publishing was "vanity press". It's good that not only that phrase, but the stigma attached to it has fallen into disuse.
I hope this answers your question.