I believe Japan has stricter emissions laws (even some of the strictest in the world) so they likely have a different exhaust setup. I know a lot of sports cars and super cars in other countries have stricter exhausts than their North American counter parts these days.
Interesting that the Protos on display at TAS also have the non sport grade muffler.
that seems like it makes sense, but if this exhaust meets lower emissions why wouldn’t they do it for the UK market rather than not sell them there?
Mainly because the 370Z just didn't sell well in the UK. That's the only reason I can see them not offering it there. But just as an example, the McLaren Senna (a UK manufactured car) has a completely different, more restrictive exhaust for the EU compared to the US production one, which is less restrictive and louder. Now this is an extreme supercar if not borderline hypercar, but the same applies for a lot of the lower level sports cars as well.
Japan has stricter emissions and noise laws (their noise laws are VERY strict relative to US). The muffler design isn't going to affect emissions, but absolutely does affect noise. I believe it's the same case for Europe, which would explain the variance with the McLaren cars pictured above.
