A couple of days back I had rallied about the academic publishing. The FUD (fear, uncertainty and doubt) is that the “sales” will be impacted. However, I doubt.
This is a plausible scenario (as below)
Imagine that person A asks a question on an Internet forum, and person B says that HOP has a section that could help with the question. If A wants to follow up, they now must find a copy of HOP. If the book is out of print, this can be difficult. It may not be in the library; it almost certainly isn’t in the bookstore. Used copies may be available, but you have to order them and have them shipped, and if you don’t like it once it arrives, you are stuck with it. The barrier is just too high to be convenient.
But since HOP is available on my web site, B can include a link, or A can find it with an easy web search. The barrier is gone! And now I have another reader who might mention it to someone else, and they might even buy a copy. Instead of drifting away into obscurity, HOP is a book that people can recommend over and over.
I find that the older editions had described certain principles better than the newer ones. The older editions may not suitable for the “newer generation updates” but consider this- classical textbooks are classics for a reason.