I'm talking about places where -40 is common. And I'm not saying that many of the 100 million have block heater plugs, I'm saying that they could -- the cold places are a proof of viability.

Michigan doesn't get that cold that often (maybe the UP does). Think Minnesota or Finland.

And the point isn't that it already covers 100 million, just that if there's a need (like there is for warming cold engine blocks in winter), it's neither particularly complicated nor expensive to provide this kind of overnight trickle charging.

I have to second this. I have lived in MN and MI for most of my life and plugs outside are not at all common.