re: In Shadow Of MOOCs, Open Education Makes Progress
Yes, where you have foundation funding to create a complete textbook, the authors do get paid.
There are really two levels of sharing, one where instructors share out of the goodness of their hearts, but that's usually more casual - sharing materials they developed as a byproduct of their teaching.
On the other hand, if you're going to ask someone to write a whole book and go through multiple edits and levels of peer review, then you need funding for the authors and the editors. In some cases, the university itself may provide support for a faculty member by letting them teach fewer classes while working on a book, or for that matter creating a series of videos or other resources.
This is not dissimilar from what's happened in the open source software world, where much of the code that is distributed freely is developed by an employee of some company who pays that person a salary to work on open source projects. There can be many other people who make a difference by contributing bug fixes or other work on a volunteer basis, but the projects are more successful when there are also some people getting paid for doing professional work.