Eeer, sorry to bring this back up but I casually looked at the wiki for “supercar” and it says:
A supercar is a luxury, high-performance sports car or grand tourer.
The term is used in marketing by automakers for unusual and expensive vehicles, and has been used to refer to at least four different sorts of cars:
Limited-production specials from an “elite” automaker
Standard-looking cars modified for power and performance
Models from smaller manufacturers that appeal to enthusiasts
One-of-a-kind “showcase” project vehicles built by custom car retrofitters (usually extensively modified collectible muscle cars or grand tourers updated to the latest “streetable” racing technology).
So, it seems the definition is pretty broad!