The supercharging actually is working at low RPM and we all know that most of the Turbo will not get good result at low RPM or we call it turbo lag, so VW thinking to get good power from low to high rpm, so they mixed the supercharge and turbocharge together, low rpm the supercharge will kick in to give full torque until certain rpm, the supercharge will stop working and turbo charge will then start working until redline.

the reason why that engine uses super is because of the small size... like gti, with 2l the lower rpms is not a prob so the turbo is only needed for higher rpms
turbo gets good results also lar, if it is made to cater to low rpms... just that if u put a low rpm turbo at the high rpms will run out of juice... usually ppl get high rpm turbos because low end power usually solve with higher cc engine
true, but usually not in small engines.... at least 2 litre and above will benefit from twin turbos... for now twin-charger is still better in the 1.4 block