To clarify, a "touch screen" responds to any pressure... i.e. a stylus
pen, finger, chopstick, etc...

Touch screens work great on any small screen device such as a pocketpc
since, when using a small device, the stylus or finger is the only thing
touching the screen at the one time.

On the larger "tablet" screens, it is difficult to use a stylus without
resting the heel of your hand on the screen itself, and, when you do so,
the additional contact of that part of the hand also generates unwanted
screen inputs.

With an active digitizer, you can comfortably rest your hand or touch
any other part of the screen and only the tip of the stylus will
generate a recognized input.

Beverly Howard [Microsoft MVP-Mobile Devices]