I think the main reason why Porsche uses AWD on the TT is torque. More than safety. And specially because the way a Turbo engine delivers Torque.

Although moderns safety systems will be able to control a 997TT RWD with not a substancial decrease on driver security, they would be continuosly talking torque away from the engine. To maximize performance from a Turbo engine an AWD system should balance the weight difference.

For example a Gallardo does not need AWD (as proven by the F430, Zonda, Ford GT...), but because they are Audi the HAVE to use it.

About racing, I believed Audi won 7 out of 9 European Touring car championships the year they introduced the Quattro A4 Touring car. They were inmediately banned for the next year, having to provide a FWD version.

And also in Racing, I am sure if regulations where not so tight they would have been using VTG Turbo engines for a while in GT racing. It does not matter how good the n/a engine is, the amount of power you can put on the ground with a turbo engine on corner exit is always going to be far superior than the n/a alternative. And with no-lag systems they would just give no chance to a n/a motor. That is why all regulations favour n/a and everybody uses them on GT racing. Le mans has been won by a Turbo Audi for many years now though.