The Oil Drum

I wouldn't be so sure about that.  A/C is a hellaciously wasteful powerhog.  Cars have a few things going for them, first of all the fact that they roll on wheels.  A lot of people have surely rode a bike before at some time.  I'm sure you know from riding a bike that oftentimes you don't even need to peddle.  If you are going down even a slight incline you can pick up a lot of speed and just roll with no effort.  

The truth is this applies to cars too, and actually you can roll quite fast on even a very slight incline as a result of the car's weight.  I think many people are under the assumption that without the engine pushing constantly the car would just stop, but that is not true (if you have a manual it's easy to push the clutch in, it can be impressive sometimes just how far you can roll with no power input whatsoever).  

Once a car is actually rolling it doesn't necessarily require that much power to keep it in motion, especially with low rolling resistance tires.  On the other hand with AC we have the issue that people are trying to keep their houses well below the ambient outdoor temperatures.  When you're trying to keep your house 20-25 degrees below the ambient outdoor temperature you are just going to waste tons and tons of energy.  It's kind of like running uphill, you are spending a lot of energy fighting the laws of nature.  An AC will be running basically nonstop during the day, whereas on average a car will not be in motion more than a small fraction of the day.