For buttons, touchability requires something different. Touchable buttons need borders. By “borders” I don’t mean outlines, (although outlines are included in my usage of the word). I mean borders in a broader sense. A button is a tappable area, clearly delineated from the un-tappable content around it by an obvious border.
I, for one, am a fan of a nice, hollow button. Betcha we see a lot of those as iOS and designers at large take a step back from the ledge.