Isn't the usual approach for these things to not use IP or wireless at all, but some other simple serial protocol like ZigBee and have them talk to a gateway "c

Isn't the usual approach for these things to not use IP or wireless at all, but some other simple serial protocol like ZigBee and have them talk to a gateway "controller" that's connected to the outside world? The last time I played with wireless sensor networks that's how it worked, and they can actually form their own mesh network.