you'll find that as far as clothes go top designers are British(English), Italian & French (although alot of americans think they have style, i don't remember the last time i saw a multinational American fashion designer which designed outside of the public market)
as far as cars go, British(general), German & Italian... although the sweedish have been known to export some nice designs from time to time.
Software - American, British(general), German
furniture - American, French, Spanish
you could go on for ages really, but the production of the designers and thier "quoted" quality comes alot from the backgrounds of who the designers are.
American Car designers, create vehicles that the American want to driver - oftenly the size of a small house and a good foot off the ground. Something that can take a pounding.
This is why i doubt you'll ever see a beautiful car design from then, and why the Brits/Italian/Germans are so good at it. We prefer our cars to have ALOT of speed and we want them to be small enough to get through the inner city congestions.
I think the adaption of using curved designs rather than lego blocks probably helps too
point is though that you can't generalise one nation saying they're the best designers... as Italians might know a thing or two about style and flare - they haven't a clue about computer design, i mean name me a single Italian Microchip manufactre?
Or how about weapons of war, how have the best designs there?
there is no one dominant nation in this field, good designs don't always = good looks.
