I wouldn't be quite so quick to ridicule this concern.
How about cars with engine stop-start? They might not be running when you park, so it would be less apparent that the car is "running". This feature is becoming increasingly common.
In addition, those of us who grew up with cars that needed to have a key turned to start or turn off are deeply habituated to the action of shutting off the car when leaving it. On the other hand, with the proliferation of remote starters, push button starters etc. there is a whole new generation of drivers who will never develop the habit of turning the key and so may be far more prone to forgetting to shut off a car. Not all of these people can be written off as idiots.
Obviously the solution is some sort of automatic shut-off, although it will have to be done carefully so as to not cause frustration when there is a good reason for a car to be running for a long time with no driver interaction. Or you Albertans will sometimes have to sit on cold seats in the winter.