I discussed this issue with someone who asks to check library and charity shop dumpsters or 'skips'. He has found first edition hardbacks of Mark Twain, J.K. Rowling, Isaac Asimov, Terry Pratchett and many others thrown out by librarians and charity book shop managers (although did put a 1st Ed. by Dan Brown back into the dumpster). In response to the 'ouch' about book age in your piece, 99% of the most collectible books in fiction (not the same for academia) are much more than 20 years old, so do forgive with good grace the few of us will not be clapping for well-intentioned book burning.