The point that is being made is that if you take a given drivetrain from engine to tires, the speed of the tires is directly proportional to engine speed (with a manual tranny anyways), thus the speed of the vehicle can be calculated from engine speed. There are no terms for wind resistance, rolling friction, etc, because they are irrelevant to this equation. That is not the same as saying that these factors are not factors in determining a cars top speed.
Basically, if you know the engine speed, you know the speed of the car and it 'ams what it ams' regardless of its weight, COD, rolling resistance, etc.
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