Printed books are not the only things that can be copyrighted. I am not arguing specifically that these books in question are copyrighted, because I have not seen them.
If I make a bunch of original sketches and notes, and I bind it and sign my name to it, and I write at the top copyrighted August 18, 2006, I can sue someone if they come along and make unauthorized copies and sell it. I may have to prove damages, and it may be more difficult than if it was a book published by a publishing house, but the principle is the same. Again, I am not saying this was done for the books in question. Just because I don't have my work published and can be bought in a book store for $20 doesn't mean anyone can make copies of my original works and sell, assuming I have proclaimed it to be original, mine, and copyrighted.
I am not a copyright lawyer, so I reserve the right to be wrong, but I believe this to be true.
Kelly