I think the answer that your looking for is that these new Bluetooth styluses have a pressure sensor built in that sends pressure information to the ipad which can be used by an app the vary the thickness of lines based on force. This differs from normal styluses which have no pressure sensitivity. Both of these also differ from the active styluses from byzero and cregle which use a combination of ultrasonic and infrared sensors in a dongle attached to the dock connector to track the stylus and give you more accuracy than the capacitive screen is capable of, these also currently lack pressure sensitivity.