This is a great, unfortunately under-appreciated point. In many ways it's similar to good responsive design – if you can't maintain the pretense that you can cram every control onto a screen, you're forced to actually think about what is most important to the person using your app.

(One bit of serendipity: sites which were designed to be accessible were ahead of the curve for touchscreens, too. Designers could fool themselves into thinking a 6px button was a good idea when they have a high-precision mouse but the first iPad made everyone appreciate how bad that assumption is)