I think it's not only the actual cost of running an activation server, but supports associated with it. (E.g. People maxing out activation count, etc.)
Seems like the best approach would be to replace the activation server with something that says "Yep, you're activated."
That way you can gather potentially useful data, and perhaps change your mind later, while not requiring any support and resources beyond 0.001% of a CPU somewhere.
That's probably the approach Microsoft is taking with their activation, not sure if Adobe incorporates similar scheme. Not that Microsoft's server always respond "yep, you're activated" but I heard from somewhere they do reset activation counts after a certain period after last activation. (Something like 6 months.)
