Do you really think they aren't? Do you think Amazon are carefully culling rare books from the list?

Although, we have to face the fact that the 'indie' book industry isn't necessarily preserving stuff either. I was recently in an old fashioned book shop in Charing Cross road, and they were selling old pictures as well as books. I was going to buy one as a present until I realised that they were pages that had been cut out of some book, because they could get more selling them separately.