The whole idea of a mouse pointer or curser is to give the user a physical representation of what they are selecting, a disembodied finger if you will. If you are using your actual finger, like what you are doing with the iPhone OS, then the whole need of a "pointer" on the screen becomes redundant and clumsy.
Desktop OS X, just like Windows, does not work on a touchscreen device once the novelty wears off.
I'm much more excited to see what developers are going to do with multitouch and accelerometer based controls. Much better suited for a device like this and much more innovative.