The S2K and G35C isn't all about "speed". People get them for reasons other than straightline speed and that's not what they're built for so you can't really count that against them. The S2K is a very fun car to drive and hugs the curves like it's on rails. The G35C is pretty quick for what it is...a luxury sports coupe. For the price...you really can't beat either car in my opinion. The fit and finish of the cars are top notch and all around it's one of the best bang for the buck.
I do agree that if you want pure speed and massive torque then an American car is the way to go. Not everyone is about speed and going fast in a straightline so those cars won't appeal to everyone, just like the S2K and G35C wouldn't appeal to someone puts speed and power as their number priority when it comes to buying a sports car.
Just like the Porsche Boxter S. I would neve spend 60K on a Boxter S but a lot of people like them and would put that kind of money down without thinking twice. Why? Because it's a Porsche and owning one makes a person feel good and get pretty much for status. You can get an S2K and beat the Boxter S in almost every single category but then you're still driving a Honda compared to a Porsche.
Different strokes for different folks I guess.