I think I'm getting it, if you have a look at my edited post.
Increased rpm results in lower manifold pressure, but a mechanically driven supercharger would compensate for this pressure loss to an extent by raising the level of forced induction exponentially.
I think!
Also, yes I know turbos need exhaust velocity, hence the dreaded 'lag' which superchargers don't suffer from too much, but it's still driving a turbine (impellor?) to force-feed air into the manifold.