I've heard and seen users whose taps on any tappable items in Sencha Touch such as buttons frequently fail.

The reason is that Sencha Touch is very sensible to any finger movement while pressing/tapping.
This is not how native iOS apps behave.

In a native iOS app you can tap/press a button, move your finger on the button and then release it and it will fire the button's action.
This doesn't work in Sencha Touch applications which is nicely reproducible through the kitchensink's "Touch Events" page. Moving the finger slightly triggers the dragstart, touchmove, drag, touchend, dragend events, but not the tap event.

What's y'alls opinion on this? Is that by design due to any constraints? Can this be improved/fixed?