Just thought I'd add my two cents:
Really cold starts are hard on many vehicle components and lead to early degradation of those components. For most folk, the coldest start is in the morning, and more often than not, one is at home, and so a plug-in heater is helpful and convenient. Of course, there will be many other times when an electrical outlet is not available, and you've got to start the car in whatever temperature you face.
But the key point is this: the plug-in heater is not usually an absolute necessity in order to get the vehicle to start; rather - it makes starting in the cold much easier on the vehicle. So the more cold starts you can eliminate with a plug-in heater the better, even if you can never eliminate all cold starts.
As a fun aside: when I was hitchhiking across the Tibetan Plateau, I got a ride in an old diesel truck for a few days. This was a decent sized truck on large tires, with pretty good ground clearance. Every morning, we built a little fire underneath the engine, and after the fire had warmed things up, the driver started the engine