Upper end Porsches do fit the "exotic" category IMHO.
Some cars are more exotic then others.
To each his own.
I agree that the sundry Mustangs, Camaros, Subaru STi's etc are not exotic. They can be made into very fast cars but not exotic.
I agree with Waxer here. Exotic cars are not just defined by the size of the engine, the look of the body, the handling or the top speed and acceleration statistics. It's a combination of those things, along with the lustworthy factor and emotions that come into it. For me, Porsche 911's DO fit into that category for me (well, the turbos and GT variants). As do Lancia Stratos' from the early 70's. And Series 1 or 2 Jag E-types (I suppose they're considered "classics" now :wink, but once upon a time they were exotics) and XJ220's. None of which have engines larger than 6 cylinders.
I don't have a healthy lust over sundry Mustangs, Camaro's, STi's etc, although I do have a healthy respect for what they can achieve.