The point is profit, plain and simple. McLaren did it with the 650S, Porsche pretty much wrote the book on it, and Bentley's been doing it for a while(how many versions of the Continental GT are there now?). And they get away with it because they're McLaren, Porsche and Bentley.
I always found that weird, but then again, I'm American. Here, you usually just get one model, then you can add various packages to it, like a Cadillac ATS. But with European cars, even if one car puts out a measly 20hp more than another and has no other appreciable differences, it's still an entirely separate model. But people still pay for it, so they're doing something right.