Here is Aaron Swartz on Wikipedia:
When you put it all together, the story becomes clear: an outsider makes one edit to add a chunk of information [to a Wikipedia entry], then insiders make several edits tweaking and reformatting it. In addition, insiders rack up thousands of edits doing things like changing the name of a category across the entire site -- the kind of thing only insiders deeply care about. As a result, insiders account for the vast majority of the edits. But it's the outsiders who provide nearly all of the content.
(Correcting Wikipedia's founder, by the way.) When I visited my editor, Marian Lizzi, at Penguin, I realized that book publishing is exactly the same: Outsiders write the books, insiders edit them.
The curious thing about book publishing is similar to what Swartz noticed in a different realm: The content, the crucial stuff, is entirely from amateurs. No other industry, with the possible exception of craft shows, is like this. If I run a deli, I buy supplies and food from people who make their living selling supplies and food. If I make clothes, I buy my cloth from professional cloth makers. If I make cheese, my milk comes from professional farmers. Only book publishers endlessly deal with amateurs.
It is the source of their power -- power to change the world. The first widely-distributed math textbook changed math forever: No longer could math teachers charge so much (since a book cost much less) and the quality of math went way up (because many more people could learn and improve it). Books and open-source software may seem to have nothing in common but Wikipedia is intermediate between them. Open-source software decreased what programmers could charge and the quality of software is going way up. (For example, the R language for data analysis.) Wikipedia decreased what scholars could charge to write an encyclopedia article and the quality of encyclopedia articles is going way up.
Books, open-source software, and Wikipedia are just three examples. Blogs are another; they are to newspaper columns as open-source software is to computer programs. I like to think self-experimentation will be another; it allows amateurs to do some types of science. Long ago in human evolution, there was no occupational specialization. Humans were like all other animals: We all made our living in the same way. Occupational specialization started with hobbies -- a hobby instinct, you might say. People have many different hobbies. We still have that instinct. It is now in the same brain as a great deal of specialized knowledge and skill (how to program, for example) derived from the specialized ways we make our livings. It is the combination of that hobby instinct (that makes us enjoy making something well-crafted, no payment needed) with highly-specialized knowledge and skill that produces books, open-source software, Wikipedia, blogs, self-experimentation (I hope), and, eventually, many other things that will transform our lives.