Ultimately, who the frak cares if GM lied? Teslas were supposed to have a multi-speed transmission, which got ditched when it was too complex.
And the point of the multi-speed transmission is to counter the problem with electric motors: they make the most torque at rest, which drops off as speeds go higher. Over 70mph, I’d bet that the electric motor they have in the Volt is pretty much maxed out, so between 70mph and the 101mph limit, the engine clutches to the generator while the generator is engaged, “driving” the car even further.
So ultimately, if the point is to use as little gasoline as possible without the compromises of electric-only propulsion, then who cares how GM designs the car - so long as it performs as advertised?
P.S. Apparently Motor Trend (who “broke” the issue of motor-driving-wheels in the first place) just posted in their blog how two trips with the Volt - one over relatively flat So Cal, the other over the mountains - netted 126.7 mpg and 74.6 mpg respectively. All in 100-degree heat with the A/C on.
In short: “The Volt, to reiterate, used 2.36 gallons over 299 miles.”