To me, muscle car and sports car are two very different things. The muscle car is a purely American thing - lots of power, pickup and great straight ahead. A throwback to the street-racing, pink slip days of yesteryear (OK, so maybe that still goes on).
The sports car, on the other hand, is something you can toss around corners and curves with minimal loss of speed and no loss of grip. Two different classes of car, for two different types of car-buying masses. Both have their place, imo.