Bryan Yeager said,
Print-on-demand has been mentioned here as one solution, which I think is completely applicable. I think publishers are finally starting to get it. Check out this demo of Wiley Custom Select, which is powered by the MarkLogic XML Server: http://www.wiley.com//college/wcsdemo/
I suggest you check out a TED Talk with Richard Baraniuk of Connexions from 2006 about open-source learning: http://www.ted.com/talks/richard_baraniuk_on_open_source_learning.html
Connexions (http://www.cnx.org) enables academics, educators, and others to work together to create their own digital textbooks on an infinite variety of topic areas, and also utilizes print-on-demand if the creators want to produce them as books.