A BMW cannot by definition be a supercar, except an M1 of course which is totally.
The problem is the definition of Supercar. Guy Kawasaki of Apple (I think) once said that "good software is like good pornography, you can't define what it is but you can recognise it if you see it" - or something like that. What is a Supercar kind of matches that dilema.
Now I got to post this and see if it appears