No, what I think is that they know EXACTLY how many have been activated (they MUST know you have an active radio if they are going to bill you, right? Your assumption that "There's no way they can possibly tell how many radio are activated" is completely false.). And they also know how many they sent a deactivation signal to (they need to STOP billing you if you cancel or transfer, right?). The difference in those two numbers would be the presumed "active" radios (those that have been activated but NOT de-activated). Since it 's pretty well known that they overestimate the count of subscribers by including those from "free trial" subscriptions with the pruchase of new cars, I'm saying that if they REALLY sent a deactivate signal to all those radios and some random advertiser asked for the numbers, there is no way they could support the number of subscribers they bill advertisers for.
If you are asserting that they really want to deactivate radios, why wouldn't they be sending those deactivations more often? Like at times when people are likely to be listening? I pretty much only listen to my radio during the traditional terrestial "drive time." You would think that would be a pretty good time send it. But maybe that's why I'm not in the Satelte Radio business.