I've heard about this, it seems to be an American phenomenon. I taught applied mathematics at a UK Russel group university for 10 years, I started each course with "You do not need any books for this course, the lectures suffice; if you want to read around the subject I would recommend [2 or 3 Dover editions at £10-15] or [a couple of classics I was sure were in the library]". Most other lecturers did the same.