RHD just because it is rare. Also remember here in the US we got different parts from the rest of the world - mesh grill, tail lights, front indicators, clock and so on. I search for parts to make my Z car different from others. I hate going to Z shows and seeing the same thing over and over.
As far as later cars in the US you have lots to do just to make one legal. Even getting one from over the boarder isn't easy anymore. Luckly my Fairlady was brought over legally and has paperwork. It must just be a US thing for it to be "cool" to have a RHD car.