I had encountered this in the lower div general education courses at my university. The most egregious one was the professor who required us to get the current edition of the textbook (since he would be assigning problems out of the new book, which was just a shuffled version of the previous version) that he wrote himself. Fitting that it was an economics course.

Once I got into the CS courses, most if not all of my professors just provided PDFs of either their own material or some open source textbook they were contributing to.

Going to guess 95%+ make use of online access codes in freshman classes. Saves the TAs for upper level classes.

> DRM-laden online books is a red flag that the college you are attending is a thinly veiled profit center, not an education provider.

So then most US colleges? Like spectralblu said, this is common in lower level classes—especially math classes for some reason.