> A bank or gas station could use a generator, couldn't it?

Local power is only the start of it for banks: the local bank these days isn't much more than a hole-in-the-wall machine with attendants, and your money is all ones and zeros in a computer far, far away. You'd need to have power going to every network relay station between here and there. (I've had cashback requests at a supermarket refused when the network is down.)

BT here are threatening to make all house phones network-based. Nobody has yet convinced me that they'll work in a power cut, even if the network hub in our house is battery-backed.