Caymen,
You are showing your ignorance again !! But that is too be expected.
The way STS controlls boost has everything in the world to do with spinning the turbo.
The typical wastegate senses boost pressure and when the predetermined boost pressure is reached, the valve opens and exhaust is allowed to bypass the turbo which slows the turbo and reduces boost pressure. The BOV (blow off valve or pop off valve) is a term primarily used in full racing applications because they dump the exhaust gas into the atmosphere. Steet turbos more often use a bypass valve to divert exhaust gases around the tubo and out the exhaust pipe and muffler, preventing the turbo from creating any more boost.
The STS tubo does NOT divert the exhaust gas away from the turbo but continues to keep the turbo spinning as fast as the exhaust will spin it. STS only dumps the boost pressure since it is only filtered, compressed air. The key advantage that the STS turbo has is that the turbo is always getting full exhaust pressure. That reduces the inertia required to get the heavy turbo spinning at full speed...That delay in getting the turbo spinning at full speed is called Turbo-Lag which is the biggest gripe performance enthusist have about turbocharged engines.
Earlier turbocharged vehicles with a wet intake system use to suck air and fuel in through the carburator or throttlebody injector system and compress the air/fuel mixture. That volitle mixure could not be just dumped into the atmosphere. Even after the universal adoption of Fuel Injection, some Turbocharged vehicles still will control boost pressure by diverting the exhaust gasses around the turbo.
With STS turbo's, as soon as you hit the throttle, the boost pressure is at or near maximum boost almost immediately and tubo-lag is nearly eliminated.
...Rich