Do you not understand the concept of Copyright?
Sure I do, and I don't have scanned books that I don't have a physical copy of. I use other reference material:
http://amigadev.elowar.com/. This would've been taken down very fast if Vesalia had a problem with it. Has been on-line for years now. Also, the autodocs are usually quite sufficient for many things.
then you can have an opinion on whether a scanned version is better than a paper version.
I can, and am legally able in my country, to have ANY opinion I want. No need for YOU to tell me what I may and may not do, thank you very much.
I own a real and valid copy of his book and see no need in a scanned version and I also have a copy of the Encyclopedia Britannica. You know they both have this old thing called an "Index."
It's great for you that you prefer physical copies, and they're great. I wish I had The Art of Computer Programming, but can't afford it right now. However, for reference manuals it's certainly a good thing to have a digital copy for getting to the information you're looking for faster. Don't see how that's so hard to understand.
I'm not advocating theft here. Buy a copy and get a digital version somehow. Or just buy the digital copy instead if available. Both options are obviously better than buying second hand, because the author won't see a dime then.