IO540,
I don't think this statement is correct:
"The normal operation of a carb (or a fuel metering unit) is that it measures the flow of air (actually it measures a parameter which is a combination of volume and mass flow) and dispenses the fuel accordingly".
I don't think a carb is so clever as to measure mass flow. Fuel is drawn through a jet or series of jets, depending on the barometric depression in the venturi. The depression is merely proportional to airflow velocity.
Also, you said that detonation cannot occur below 75% power. What basis of fact do you have for that? In my experience, piston engines can suffer from detonation at much lower power settings, depending on the load on the engine.
Hence the requirement to remember "RPM max, mixture fully rich, carb heat cold".