No, my point is that GM could build a "0-60 in 3 sec." Vette anytime they wanted. Marketability, though, as you point out.
Yup, the C5R and the C6R. They have won GTS for the last 4 years.
Well the 0 to 60 times are impressive but as you point out Corvette's and even Dodge demons can be made to do a fast 0 to 60.
The design of a Saleen or McLaren isn't to accomplish a fast 0 to 60 time. That is a byproduct of having a light, balanced (see mid-engined) car that can accelerate, turn and stop.
So while many cars can be modified to do a fast 0 to 60 time, very few can every offer the full spectrum of performance that a light mid-engined sports car can offer.