That said, you are right that my point goes primarily to college and graduate textbooks, where changing a few lines here and there qualifies for a "new edition" that makes all the other almost identical previous editions "obsolete." And I have no problem with professors or anyone else making money off their knowledge.
But I also have no problem with calling B.S. when there is a much cheaper path to the same knowledge.
It was quite clear, I hope, that the point was not whether there exist a professor that wrote such a textbook, but whether that is a phenomenon pronounced enough that you refer to authors as professors..
As I like to rant upon more than one occasion, there has been nothing new discovered in mathematics below the MS level in the last 100 years. Any math text from the last 100 years that has been successfully used in grade or high school teaching will suffice for the next 100+ years.
I’ve long been infuriated with the “methods” crowd that keeps wanting to change texts to comport with the latest educational “methods” fads that sweep through the schools. A lot of grade school math is taught with repetition and drills - what the methods people like to call “drill and kill.”
Well, as I tell them, if I had to even think about basic computational math as an engineer, I’d be dead meat. So yes, I believe in drill and kill. Kids should be able to rattle off the multiplication table up to 15x15 without blinking an eye, IMO. They should be able to whip out long division easily. We could alter how much geometry proofs are needed, but every kid should have a couple years of algebra as well as a full course in basic math, including business math, before they graduate from high school. None of this math has changed in the last 100 years. We should find a text, agree on it and just use it in all schools at that grade level, and keep using it year after year.