That's not to say it couldn't try to guess, though. Not that I'd have thought of this unprompted, but low bandwidth, high latency, and an IP address (as seen by the update server) assigned to a mobile carrier. Seems like a good time to throw a pop-up and say "We think you might be tethered. Are you sure you want to continue downloading four gigabytes?"
As an aside, and if it doesn't already, DHCP should have some way of altering clients that they're on a metered connection.
Definitely worth a read. I misplaced my copies during a move many years ago but recently got them all as e-books. Unfortunately, they weren't quite as good as I remembered.
