You'll have to prove that. Wind resistence increases geometrically, so I'm not buying it. It takes considerably more energy to push a car at 70mph than it does at 50mph. I'm not buying it.
We're in agreement about increased gas usage at higher speeds as it relates to wind resistance. It can be seen in "human terms" on a bicycle, too. To sustain a speed of 24 m.p.h. on a bicycle is TREMENDOUSLY more difficult than 20 m.p.h., even though it is a measly 4 m.p.h. difference.
~ Blue Jays ~
Power to weight ratio has a lot to do with it too. If you have relatively high power vehicle with a relatively low weight (12-15 lbs per hp), as long as it is not geared too steep or accelerating too hard to get up to speed, decent fuel economy is essentially a given, and while youre right wind resistance does increase geometrically, it doesn't overcompensate for a decent power/weight ratio in detracting from fuel economy. Add the higher speed/fuel efficency powerband, and the fuel efficency factor is not adversely effected by speed unless you are way up there in velocity, like 95+mph or more.
From Nashville TN to Baton Rouge, LA, going I-40, I-55, and I-12/10, doing 65 on the trip down I averaged 20.98 mpg. From Baton Rouge back to Nashville, I did 75-85 most of the way, depending on where I was (didn't do much over 80 in TN for fear of the lawman), and I got 26.35 mpg.
There are other major factors beside wind resistance at play, and if you only look at one factor of course you will get the wrong impression. The efficiency of an engine can vary dramatically across its range, with the optimally efficient speeds being set by the design engineers -- even taking into account wind resistance.
To put it another way, the increase in wind resistance from 60 MPH to 70 MPH is less than the differences in effective output and efficiency of the engine in that same range. Wind resistance is far from being the whole story.
The whole point of diesel-electric rigs or hybrid engines is that the engine can always be running at its optimal efficiency point by decoupling engine output from motion on the road. Even given the significant losses in two-stage conversion process, the much higher efficiency of the combustion engine running optimally more than compensates.