The documentation states that some components like DropDownList are not mobile optimized. This doesn't mean that they aren't touch enabled, it just means that they do not have mobile optimized skins.
These mobile skins have better default sizes so it's easier to click on them and they are also optimized for better performance.
Off the top of my head the spark desktop components that currently have mobile optimized skins are:
All components deal with mouse events (like mouseUp/mouseDown/click) in both mouse and touch interactionMode. Check out the "Mouse vs Touch Events" section of the List, Scroller, and Touch Gestures spec for more information: