...while leaving students on research-assistant salaries, as opposed to giving them any IP rights in the material that wouldn't have existed without their research and work. It's happened to people in the engineering and biosciences departments here, and I doubt it's different other places.

Yep. You pretty much sign over all your IP rights when you get hired as a grad student, anywhere. If you're lucky, you'll get founders' stock in the spin-off if they recognise that they need to hire you in order for the company to be successful. Planning for this, however, means hiding key pieces of your research from the academic community. It's quite a scam.