That's a big "+" on your figure - it's about 300 Watt-hours per mile, or 3600W constantly, if you're going 60 mph. For comparison, one horsepower is about 750 watts - a Tesla is a very low-drag car.
Anandtech reported [1] that the TDP of the whole board is around 250W. The Tegra SoCs are probably around 10W, but that doesn't get you much in the way of GPU horsepower.
Yeah, in the wrong direction, I underestimated the powertrain consumption, so the power cost of the computer is relatively even smaller.
The point I made missed the point though, it apparently isn't the energy consumption they are concerned with, other people in the thread are pointing to limiting/getting rid of the heat being the main concern.
Seems indeed, and in fact an A/C will eat a kilowatt or more, but...
The components of this system need to generate next to zero heat and they need to be placed in all sorts of inconvenient locations. That's causing automakers to desire extremely low-power dedicated circuitry over GPUs.
Consider as an example the C7 Corvette: despite its enormous blindspot, it still doesn't have blindspot indicators because they can't find any way to cram existing sensors into the thing. There are more examples, that's just the one with which I'm most familiar because I balked on purchasing one over this despite an insanely great deal on it at the time.
The powertrain uses 300+ Watts, so it seems like a manageable number if it is correct.