Giving it a fair shake?
"That said, any effort to lighten the backpacks of students overloaded with hefty textbooks, along with making it easier for textbooks to be updated as scientific progess and historical events warrant, should be given a fair shake."
It's a solved problem. We call it "The Internet". Perhaps you've heard of it. Apple's product managers clearly haven't. Perhaps their walled garden is so effective that they've forgotten the outside world exists.
Factual material lends itself *extremely* well to websites because it has an extremely long shelf-life and no copyright protection.
If something is true, it tends to remain true. This is provably so in mathematics and certainly true in practice in science and engineering until you are well past undergraduate level. Indeed, it would be rather scandalous if this weren't true across the board, since that would imply that we were teaching students something that won't be any use in twenty years time /even in that academic discipline/.
Similarly, if something is true, you can't copyright a statement of the fact. Others are therefore free to take "the truth" and present it in their own way on their own web-site. Experience shows that quite large numbers of people do this quite voluntarily and there are whole web-sites devoted to small articles about stuff.
And lastly, increasing numbers of lecturers put their course synopses online. These summarise exactly what students need to know for exams, which is a convenience you'll never get in a textbook. (I'm assuming that most students, for most of their courses, mostly just want to pass the exam and move on to the next stage. Is that too cynical of me?)