They use a capacitive touchscreen, which provides non-paired point data (i.e. x1, x2, y1, y2). So you'll find the only true multi-touch gesture they support is pinch. They can tell you have at least two fingers down, and can tell if the two outermost fingers are getting further apart or closer together, and where the aprpoximate midpoint is, but that's about it - they can't truly do multi-touch. For example, fire up the ons-screen keyboard, press the shift key with one finger and try typing any another key. You can't. It's a modal-shift keyboard in large part because they can't tell the difference between (X1,Y1)(X2,Y2) and (X1,Y2)(X2,Y1).
One big advantage of capacitive over the more common resistive is that optical clairty is far better, as evidenced by the super sharp display on the iPhone.