POD, of course, stands for print on demand, but the digital publishing technology means that any author now has the right to publish his own books -- he can indeed demand to be published.
Since the advent of printed books, authors have been at the mercy of technologies that make them dependent on others. Even before the mechanization of printing presses, the laborious process of typesetting meant that it was never economical to print a single copy of a work. Now, while the machinery to produce a bound, printed book still requires a big capital investment, it is available to an author at an affordable price because the typesetting itself is digital, and in fact, essentially performed by the author. The threshold for e-book publishing is much lower again.
It doesn't take a genius to see how revolutionary this is. The legacy book publishers -- this is what we must call them now -- will continue to hold sway for a while yet and may survive in some form. Those authors who have successfully jumped the hurdle to mainstream publishing have a vested interest in defending it, even though some of them have begun to realize that they don't have to divert part of their earnings to maintaining the huge overhead of the publishing houses.
Still, you have the example of the International Thriller Writers, launched by established authors to "help" newcomers. Curiously and amazingly, however, they still want to limit membership and promotion to authors published by "certified" publishers, keeping the unwashed masses of self-published authors at bay. Though apparently they are reconsidering their membership criteria, it seems to be a slow reaction for a genre that is particularly well-suited for self-publishing.
I had jumped that hurdle and had three books published by mainstream houses. However, this does not always work in your favor for later submissions. Whereas an unpublished author can enjoy the benefit of the doubt, a published author has a telltale record. It's not exactly three strikes and you're out, but if sales of three previous books have not been compelling, it could tilt the balance against getting a fourth chance.
I muddied the mix further by not sticking to the same genre. A key facet of publishing today is the brand-naming and franchising of authors. So you have the somewhat ridiculous spectacle of books still coming out under Clive Cussler's name when someone else is doing the writing. But it works, the books still sell. But I was all over the ball park -- publishing first a nonfiction book on economics, then a financial thriller, then another nonfiction book that defies easy categorization but is nothing like the previous two. So what niche can you put Darrell Delamaide into?
Now comes an historical thriller that really has nothing in common with the previous three books. Except that I wanted to write it. I know this book is at least as good as much of the stuff that is coming out from mainstream publishers (yes, yes, every rejected author knows that), and better than a lot of it. But, among other things, I'm not keeping my "brand name" in sharp focus.
Self-publishing is not immune to this phenomenon, of course. The most successful indies are the ones who build a fan base for a certain genre and then feed their fans as rapidly as possible. But at least now the author has the possibility of trying to connect with an audience for any book he or she wants to write. Now an author can publish on demand.