I stopped by the dealership where my Brabus will be delivered. It's a new dealership, which just opened, and there happened to be a regional Smart representative there (forget his name... but Dave comes to mind). I asked him why 16's in Europe and 15's here.
His response was the bigger profile tires on 15" gave better crash test results on the front end. Something about the tire absorbing more impact.
Not sure if I believe it or not, but that's what he said. Let the discussion begin...
BTW, the brabus rims look better in person than in the pics.