Achieving .159 Cd isn't really that difficult at all. I'd bet that any one of the hundreds of aerodynamicists employed to work on Formula 1 cars could develop a <0.15 Cd shape in no time. In fact, they do it all the time!
I'm sure many of you have seen a diagram comparing a small circle to a large airfoil, with the description mentioning they both have the same drag. Any Formula 1 car you see will have airfoil A-arms (wishbones). In fact, when I sat down with the lead engineer on my FSAE team last year, we calculated that we could save around 40 pounds of drag at just 40 mph, just by switching from round tubes to airfoils for our suspension components.
As far as automakers go, it's the market that directs their choices, not good engineering principles, as several of you have already stated. :/
However, if you study what automakers are doing to keep conventional car looks, while improving aero, you'll find that they are getting quite creative! For instance, the Toyota Corolla:
Look at the rear end of the car, it's quite boxy, and looks quite awful for aero, but you don't hear any Corolla owners complaining about trunk space or rear leg room do you? Look closely at the hard line on the outside of the rear reflectors, near the bottom outside edges of the bumper. That hard line is actually a technique that automakers are using to reduce drag by actually inducing turbulence in the boundary layer of airflow
early, thereby allowing the air to move into the low pressure area behind the car in a much easier fashion. It's quite clever, keeping the engineers busy, business people happy, and oblivious customers even more happy with their mpg numbers, multitude of passengers, and trunk full of crap.