As you say, it is next to impossible to ask good programming questions from a handheld device (I agree that SO is quite different from, for example, travel.SE). Valid mobile use cases involve searching for and reading existing answers, and commenting.
However, the "mobile" apps also run on computing platforms which are more appropriate for asking questions, such as netbooks. It's not worth the technical effort to try and differentiate one Android device from another.
Besides, as the comments point out, removing the "Ask Question" button from mobile apps wouldn't have much impact on the total volume of bad questions.
