Yes, it wouldn't really.
Right now the way this works is that a human body absorbs a certain about it wifi signal, so of the signal strength in a room dips and comes back up, someone walked through the room, for example. Couple this with what IPs and MAC addresses the router is connecting to, and Verizon can tell "human with laptop," or "human watching TV." So just "human body" or dog/cat are what it can detect. Verizon does try and sell this as a feature, as in a shit security feature.
So for cell towers, they're too far from people in an already chaotic environment to really be useful. Trees, cars, and a million other things can throw off trying to detect already minute changes in signal density. Not to mention that the signals from cell towers are much stronger, so harder to detect the changes.