Academic says used textbooks are cause of high prices

With college students headed back to class, there's more grumbling than ever about high prices for textbooks.

Some colleges are building online trading systems for students to swap textbooks. That could cut into our business, since many students buy an extra book or two while they're buying textbooks.

And here's another "solution" that threatens to cut us out of the loop: Site licenses for textbooks:

Just as software companies typically “site license” to colleges, so should textbook publishers. Here’s how it would work: A teacher would pick a textbook, and the college would pay a negotiated fee to the publisher based on the number of students enrolled in the class. If there were 50 students in the class, for example, the fee might be $15 per student, or $750 for the semester.

It's an interesting idea, but I wonder if the professor is suffering from ivory tower syndrome. Publishers already have students locked into buying textbooks for $120 a pop. What incentive do they have to rent the textbooks for $15?