I was one of those kids that was told to wait in the car a lot. I remember in the summer we were so hot we had to open the doors and sit half outside to get air. Somebody could have easily kidnapped us. I also remember those damn child locks that kept us from getting air. We boiled. And if we stayed in the car in winter we either had to find a blanket, the one that was supposed to stay in the car but was usually in the trunk, or we had to curl up and try not to freeze. I imagine that dogs feel the same way.
Cagneydog mentions that the dog "enjoys" watching people. Maybe he's just seeing if any of those people are his owners trying to get him out of this predicament. And sleeping in the car is enjoyment for a dog? or is it just that he gave up and is trying not to get too hot. I've seen dogs pulled from cars unconscious because of the heat. The owners or people who find the dog have to tap on the windows to see if its sleeping.