"Matthew S. Whiting" wrote in message
...

Doesn't ATC have to take SOME action to confirm your arrival?


Only if you consider watching the aircraft land to be some action.



If not, how is that different from a landing at a non-towered airport
on an IFR flight plan?


At a non-towered airport ATC is not able to observe the pilot land, so the
pilot must tell ATC he's landed or cancel IFR.



How does the computer know the difference?


The computer doesn't need to know, there's no computer processing beyond the
destination airport.

If a pilot cancels IFR while enroute the controller receiving the
cancellation will enter a "remove strips" message, every ATC position
downline that has received a strip will receive that message. If you're the
last controller, tower controller at a controlled field or the controller
providing approach control services for an untowered field, there's nobody
to pass that message to.