That's my understanding too, or rather that Americans say convertible and Europeans say cabriolet.
My vision of a "Model C" would be 2-door 4-5 seater with a convertible top, something like how Volvo C70 convertible is based on a boring sedan (no, I'm not calling Model S boring). A 2-seater convertible is just too impractical for me, need a backseat, even if it's just a small one.