Apple uses Capacitive Touchscreen for its iPhone; while Windows Mobile Phones (Even Nokia 5800 uses Resistive touchscreen), uses resistive (or non-capacitive) touchscreen. The benefit of resistive touchscreen is that it responds both to the stylus and to a finger, making it suitable for both general prodding and the sort of handwriting input (dont know how many prefer that). The downside is that the resistive touchscreen feels less precise and responsive than the display on, say, the iPhone (capacitive one). A slightly-flexible plastic front is necessary, rather than glass, for resistive touchscreen and the fact that it responds to finger pressure means scrolling isn’t as smooth as on the Apple handset.
Most obvious reason for manufacturers using Resistive Touchscreen is the cost factor. Is it so? It can't be that. USD 10-15 difference between the two technologies cant be such a deterent. Even the newly launched HTC HD Touch at USD800+ uses Resistive touchscreen.
I have used both iPhone and WindowsMobile Phones, and can say for sure that the gap is huge in terms of how they respond to the human finger touch. Till Windows Mobile phones start coming up with Capacitive touchscreens, they wont be as smooth as iPhone in finger writing and that is half battle lost.