Nothing new here.aerodynamics help, but the best mileage is obtained with low weight and having the cruising speed geared to the lowest BSFC point of the motor (usually close to the torque peak), while using most of the power the motor makes at that point. In other words, really slow.
In the late 70's the CVCC weighed 1900 lbs and had 70hp, the 2011 Civic DX is 2700 lbs and 140hp, and that's considered a light and slow car by today's standards. Most of the extra weight is federally mandated safety equipment and power accessories. Add in the fact that most people want faster vehicles with gee-whiz features, and mileage is going to suffer.
Anybody seen a VW 1L in this country? Didn't think so.