Its all about perception, im not sure if i would call a NSX a supercar or not. Probably not as it goes, for exactly the same reason i wouldnt have a Lexus in any shape or form over a Jag/Merc/BMW.
It's definitely a personal thing, everybody has their own perception of what a supercar is, so with no hard and fast rules it's easy to twist preferred marques or models into the supercar category.
The 911, R8, Z06 etc are not supercars, but you'll see them referred to as such in plenty of places. The NSX doesn't cut it either, but that's my opinion...someone like LJK, somebody who knew better than most what a supercar is, would tell me different. Not being a supercar is in no way a detraction from the Honda, I'd much rather have a NSX than a few bona fide supercars I can think of.