kW/kWh aren't commonly used outside of electrical applications in the US, so people are less readily able to quantify and compare in other contexts. Looking at a variety of natural gas companies' bills, you'll get volume multiplied by a therm factor instead of simply using kWh; horsepower for not just cars but even electrical motors and pumps.
I think the average person will have looked at their electricity bill and put the basics together about watts and watt hours. As for comparison with natural gas, I think he didn't touch on the real metric people then turn to- cost. Depending on the state it can be much cheaper to use gas vs electricity.
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