I can understand their thinking with this. Image is everything and when you hear someone say a "Chevrolet Corvette" it sounds more "sophisticated" (or something) than saying Chevy or Vette.
Now people will still call it Chevy or Vette, of course. It's not likely you'll hear someone say, "Check out that Chevrolet Corvette!" But you've heard plenty of people say, "Nice Vette!" However, if you see a TV commercial that says "Presenting the 2010 Chevrolet Corvette" it does sounds pretty awesome.