Upon reflection, this is my guess:
The AD2 client has tight integration with their store, showing you the kits you "own" as well as the other kits they sell. My computer is internet connected, so every time I launch AD2, it connects with their web service. If the Cakewalk subscription lapses, it would be easy for them to disable ownership.
Given that 99.5% of computers are on the internet, the only way to circumvent the copy protection would be (might be) to not connect. Then it becomes a question of whether AD2 validates every time it is launched. My guess is yes. Or at least there is a requirement to validate on some interval.
Its also possible that they don't have the software part of this worked out yet. Someone could buy and cancel a 1mo sub to find out that they have AD2 now, but at some point in the future it could go away. The fact that they are mum about how this works shows that they are not in a hurry to explain it. This would discourage this kind of intent.
What is clear is that AD2 it tightly integrated with their web service and it would be easy for them to disable kits if connected.