The short answer is, yes residential and business services are metered DIFFERENTLY.
In most cases. In most cases residences are NOT charged for anything aside from
in-phase current. If you draw a large reactive current you are not charged for that.
Most business, and certainly those that use polyphase power, ARE charged for both
reactive current and real current. A further difference is that business typically
have a "peak demand" meter that charges a continous rate, proportional to the
largest peak current draw in some fixed time period, like 24 hours or so. Residences
rarely have that.
"If a device is running on 240 volts, would its current consumption not be read on a single leg? "
Yes. The current in each leg is the same. The wires have to carry that current. But the
power company effectively figures out how to charge according to the number of energy
units (say, joules or BTU if you wish) the service provides, and the loads dissipate.
You get charged the same if you run a 1000 watt heater from 120 volts, or if you
ran it off a 240 volt connection.
For the sake of this discussion, I've been fiddling things a bit, the fiddles are:
1) your electrical service is center-tapped 240 volts, with 120 volts between each
hot leg and the neutral.
2) your loads are purely resistive, not reactive. So your 'power factor' is close to one.
Some of the discussion cropping up right now, involves deviation from one or both
of those boundary conditions, that I have arbitrarilly chosen, to simplify the discussion.
Jim