Max_DC
Opel is German. Developed and manufactured in Germany. While they might belong to GM on paper, they have nothing in common with the American cars of GM.
Actually, Opel
does have something in common with the american cars of GM, as in, many of them are based on Opels -- for example, the Cobalt is heavily Opel-based. Even its styling is a little Opel-esque.
@Definition of a sportscar: The Audi RS4, Subaru Impreza WRX STI, Mitsubishi Evolution, M3, and Nissan Skyline GT-R aren't sportscars. They're sports sedans. It may seem trivial, but if you want to talk about true definitions, it really isn't.
The original definition of a sportscar was a 2-door, 2-seat, front-engine, rear-wheel-drive, open-top car with spirited handling. A powerful engine was a plus, but not a necessity.
The meaning has changed over the years, and as I understand it, "sportscar" is now defined as a car with 2 doors, rear-wheel-drive, excellent handling (not always numbers, but also the ease with which corners can be tackled), and more of an emphasis on performance than practicality. The Miata is a sportscar. The Skyline GT-R is not (it may have 2 doors but the chassis is available with 4 and the car has a decidedly different shape than a coupe like the 911). The 911 is a sportscar. Aston Martins are not (they're grand tourers, more at home cruising on the highway than carving down a mountain road). The Corvette is a sportscar. The Mustang is not (the Mustang has always been more about straight-line performance than cornering, but the newest one challenges that tradition).
It's silly, but as far as I know, that's the way it goes.