I don't think that demonstrates that at all, but even assuming it did: when they do so, they get diabolical gas mileage.

Top Gear did an amusing test where they had a Toyota Prius drive flat out around a track, with a BMW M3 (a larger, heavier sports sedan) keeping pace with it.

Over the course of the test, the Prius returned 14.3 miles per gallon; and the BMW M3 achieved 16.1 - despite the fact the BMW has a 4 liter turbocharged, six cylinder engine vs. the Prius 1.5 liter, four cylinder.

To be fair, that test way way above legal speeds. I don't think it's representative even of motorway performance.

I don't see your point however - what I'm saying is that at 130kmh (standard motorway speed in most of europe) a 70-90hp subcompact (by far the most common car in europe and the world in general) is running at above 80% max power (testified by the fact that as soon as there's a significant incline their speed will fall back to 110-120). So running long times under heavy engine load is quite normal for cars