Add me to the chorus! It baffles me that I have so many fast elegant trackpad gestures for navigating my laptop, while I'm forced to essentially mimic a "point and click" interface on a touchscreen. Granted much of the additional functionality on the laptop is gained through bettertouchtool, but it's still such a wasted opportunity.
It doesnt make sense from a fitts law standpoint(small button targets, longer travels for your hand), nor does it make sense from a screen real estate perspective (having to dedicate already limited space to a persistent ui).
And to the argument that users will be confused by invisible tools, it seems users get by quite intuitively with no zoom or rotation sliders, and in fact already have experience with back/forward navigation swipes in calendar, iBooks, photos, etc.
Between gestures and voice input, apple seems to be making a habit of introducing novel ui paradigms to users and then leaving them to languish in half-realized implementations. (ok maybe a little dramatic, but you get the idea!)