Well I want to thank you for being polite. I was being dismissive when this started.
I agree with you strongly on the value of open source prek-college textbooks with lesson plans... I think that's a huge advantage. And I agree there isn't much value in the proprietary stuff no reason the content couldn't be open source. Open source content would obviously want to be something like HTML5, though specific versions like interactive iBook format could also be created as derived works.
Even the apps that have tablet specific version, no doubt share much (if not the vast majority) of the software. They may be separate apps for commercial purposes, or saving space in terms of higher resolution icons, sprites, etc.
That's not the case at all on iOS. They are genuinely different versions with different functionality. Here is a link to an article with 20 apps iphone vs. iPad version side by side. You can see this is a different GUI: http://www.cnet.com/pictures/a...
When done right, the apps written in cross platform environments are not noticeably slower than apps written specifically for one architecture in all but the most resource hungry apps.
It is not just slower it is things like memory usage, and how they tie with other applications. For example an iOS application you generally are going to want to use iCloud integration to automatically tie information between: iPhone, iPads, Macs and (potentially) the watch. On Android you are going to want Google integration and tie it into Google's excellent application framework. Those two systems are nothing like one another in how they handle data.
Or for another example on iOS you are expected to draw icons and controls at specific resolutions while with Android you are expected to use vector graphics.