The assumptions. Everyone has both an Intel machine running Windows or Mac, and a machine running iOS or Android.

Wrong. Linux on ARM gets you so far and lets you do almost anything you want. And then when you have to interact with the outside world, you run into assumptions. What if I'm not running iOS or Android? What if even your Linux app doesn't work because you assume I use Intel? How about everyone offer at least an HTML5 app and if you want to make proprietary crap on the side, you can?