Particularly when it is available online for free at http://mitpress.mit.edu/sicp/full-text/book/book.html
For a normal book, you have cheapstake buyers, and then buyers who will pay a premium for a nicer book (hardcover, newer, etc). Now take the cheapstake buyers out of the market because they're all accessing it online for free. Economic magic does its thing, and the market price is now much higher.