As I have come to understand blowers, a supercharger, much like a naturally asp. engine must reach peak rpms to acheive rated hp(less boost at lower rpms, more at higher) whereas a turbo, once it has spooled up, gives about the same boost no matter the rpm(be it 4000 or 6000). Therefore, because a supercharger drains the engine(belt driven) and provides boost at idle, asupercharger will give you more grunt off the line, but a turbo which spools off the exhaust gases will begin to pull once you get moving and will provide you with an extra kick in the higher rpms. (my friend's WRX just keeps on pushin in those high rpms, whereas my Mustang's/GTO's power starts to fizzle at higher rpms)
But, this is how * I * undertand it, if anyone wants to add to/change my understanding, by all means please enlighten us all.