To be (kind of) fair to the bookstore, they don't make any money off textbooks when they sell them (and the amount of work to sell textbooks to an entire college/university is amazing for something they make no money from), so I'm not surprised they try to make some off of renting.

This is brought to you by my experience working in college bookstores and dealing with both textbook publishers and students.

Textbook publishing is the world's biggest racket.