On iOS devices, the "drop down" control is rendered as a large-target control that takes up half the screen and allows the user to swipe through the list easily. Whichever item is in the middle of the reticle is selected. This way, you only need to touch to activate the control, swipe to select, and touch again to confirm. These touches aren't superfluous since they all serve a clear purpose.
Combo boxes, where you can also type to select an item, seem unnecessary on touch platforms with controls like the above since it's far easier to swipe your way through a long list (especially with phone book style index selection like iOS has) than it is to scroll through a drop down menu on kb/mouse platforms.