QUOTE (Bigity @ Feb 8 2012, 07:34 PM)

That's what I had thought, so the 'quality due to the scan' statement had me a little confused.
Some of the images look good on PDF, but when printed the resolution gets a little weird, that's what is being talked about. New PDFs are based on the original work, while older books have to be OCR (Optical Character Recognition) scanned and proofed, which takes a lot more time and work, but also makes them searchable as well.
If the words are only saved on the PDF as an image (Just scanned in, no OCR), then it's not searchable.