My biology prof did this, with the exception that she had written a workbook and our homework was filled out on the pages. This meant we were paying for paper to turn our homework in on and the book was unable to be sold back.

I think this is how more textbook publishers are going to go.

My wife bought a "textbook" for a language class and it was, and I kid you not, 300 loose pages with binder holes punched in them. See, it's a textbook AND a workbook! And sure, some of the pages were workbook pages. But there's no way any bookstore would buy that back as soon as the shrinkwrap was broken.

Departments do do that - usually because they are short of funds and the money raised is used to fund consumables for lab classes. The university cannot raise a surcharge for certain classes, but they can sell equipment (read: course workbook) for that class. It's iffy, but still on this side of fine, no one makes a profit of it.

There is no excuse, though, for having to sign up for an account with a commercial publisher for exercises that are a part of your grade in that class. Normally you would pay a bunch of TAs to administer and grade the tests, but the university is too short of funds for that. So they outsource the grading to a commercial entity.