This is true, although I highly doubt companies would take this on for the perceived fear it could be hacked, but then again this is likely the fear of going electronic in the first place (although anyone really interested in pirating a 500 page textbook would simply buy a double-sided fax-style scanner - where it rolls the page through - and simply cut off the spine of the book).

A cunning use of a private tracker would be to embed a reader into the client so that non-nerds are more likely to keep opening the client to use their textbooks and simply set the seed rate low at 10kb/s so it doesn't kill peoples bandwidth and get noticed. If you make it readable in part and download in priority (first pages first, obviously), you might only have to seed >0.1% of the estimated bandwidth usage to get everyone with full books.

Actually this would be an amazing way to distribute a game too. If the client is built into the game launcher, simply have the client only download the core and the mandatory tutorial. If someone goes down a certain quest path you prioritize the later portions of the quest before continuing the download of the other quests. You could also prioritize associated quests and follow on quests because you know people will complete them.