It's kinda stupid, yeah. If it would have been the naming scheme for Europe since the first game I'd understand it, but this way it's just... I don't really know what they're thinking. What's the purpose of the added "Bros." anyway? Do they have to make clear that Mario and Luigi are brothers? I don't get it.
That said though, I'd love for them to have regional titles again like they did for Partners in Time and Bowser's Inside Story. "Voyage au Centre de Bowser" is still one of the best subtitles I've ever seen, given the context.