What the hell are you talking about? The device has a windowing system that processes events it just gets the events in the simulator from a mouse. Why's that so hard to understand and what are you talking about by "registers?"
The simulator is a cocoa application that takes cocoa events from the mouse. There's no reason why the same events couldn't be generated thru driver on the device when the mouse is paired with the device.
"registers?"
registers
Simulation software
You could use a flight simulator with a mouse but God help you if you try to pair your mouse with a plane!