If I buy a movie on DVD, newspaper, book, notes or whatever I should be able to sell it no matter what the "fine print" says. Some western European countries even let you make copies of someone else's material for "private use". I don't say it's fair though.
However, when you go to the university you normally (?) try to buy books from old students. From a student's perspective, why should books/notes in aviation be any different? The schools are already "protected" since it's compulsary to attend an approved course. If that wasn't the case, you could just buy the books/notes second hand (as with any other course) and go to the most competetive revision course if you feel like it.
That being said, I think that generally speaking UK ground schools are by far the most competetive in Europe. They do a great job and shouldn't have to struggle with students copying material illegally. Especially since many of the organisations have employees helping students out on a forum like this for free! A much bigger issue is that most JAA member states refuse to apply JAR-FCL1/2.065 (training in more than one JAA state) in order to protect its own training organisations.