I teach a university course that uses an open-source textbook. PDF or HTML version are free, printed softcover is under $25. Typically, at the start of the course about 20% of the class decides to forego the printed copy. That number usually dwindles to about 5% by the time the second test is given.

Like it or not, students still appreciate a physical book. (And these are students who have always known the internet.) In addition, reading habits differ by medium. Cushing has made a very foolish decision.