Let's be honest, historically these "updates" have always been for the sake of publishers making coin year after year. Plenty of things, at a grade school level, need no updating. Literature? Pretty much the same as it has been for years (even though textbooks are constantly updated). Same goes for Math, History, Geography, you name it. The only thing that is constantly evolving is sciences, and even those don't often find changes warranting a k-12 book chapter be completely re-written. I just don't think k-12 textbooks getting terribly outdated. For most subjects, and update every decade or so is certainly sufficient. That's a lot more time than the average iPad would last in school I suspect.