It has to be noted that the number of pressure levels is determined by the pen not the tablet. The pen transmits the pressure level to the tablet through radio waves to a grid of transparent wires in the display (basically the same concept as RFID) or over Bluetooth.
The Magic Drawing Pad is an Android tablet that is particularly suitable for use as a drawing tablet and can thus differentiate between a particularly large number of pressure levels. It can also be used completely independently of a PC.