why do you guy's like a turbo vs a centrif Supcharger?

A while back I spoke to the Supercharger Store about a procharger. On the paper where I had his # written down there was a number, $4350 for a d1sc unit complete for a bb. Was told it would support up to 900 hp. Don't quote me on that price though. I downloaded a price sheet from SDCE a while back, for a complete TT SB set up it was in, damn computer is acting up so gotto go.....try this again, the price for one of the SDCE TT SB kits was 5218.00 and that was with a non-recircualting waste gate. A local shop quoted me an "off the top of his head" amount of $7k, included in that price was stainless steel headers and as he put it, a decent ball bearing turbo......keep in mind it was a while ago, 6 months or so, I got these numbers....