At Mark's suggestion, I sent Martin Evening a note asking his permission to leave the link up. Here's what he said:
"That is no problem as far as I am concerned and you can quote me on that. The source in this instance was from Peachpit's own site and therefore totally legit.
What has happened in the past is that copies of the DVD I used to create for my Photoshop book were getting copied and sold on eBay etc. Therefore, it seemed best to make sure people were aware that all PDF content wad an extra free bonus and not needing to be purchased. It still seems a sensible precaution, but in this context sorry if it caused you to worry."
So, as far as I'm concerned, all's well that ends well, but I'm sorry I didn't see the faint disclaimer in the PDF, and I thank Mark for calling it to my attention.