Don't take this article at face value.They contrive and assume to much and they overgeneralize everything.Speed vs MPG is very much a car-by-car deal. Obviously there's always a point where physics win and you start seeing decreases. But it's different, and by different degrees, with every car. Their numbers are useless to anyone not driving a Camry or Mountaineer.
The Versa is probably a good example of a car that would fall somewhere under the umbrella of their generalizations since it's tall, a hatchback (well, the hatches are... ), and not particularly powerful. When you have little power moving a big surface area at high speeds, you're going to loose.
It's noteworthy that my Maxima logged it's highest-ever fuel milage on a non-stop freeway-only cruise at 85mph average. I've never--before or since, even on that same stretch of I-15--beaten the 31 mpg the car managed that day. I realize that there are a LOT of variables that can affect milage calculations, but gains are not losses, and the article predicts losses.