I know I'm joining in the discussion late, so I apologize if this has already been said.
My take on auto manufacturers is this: Toyota, Japanese. Honda, Japanese. Mercedes, German. smart, since it's owned by Daimler, German.
While all of these, and many others, 'manufacture' vehicles here in the U.S., they're still vehicles made by companies owned outside the U.S.
"American" cars are limited to Ford, GM and any others whose company is a U.S. based company. Currently Chrysler is in this group as well, but if Fiat ever becomes the majority stockholder, who knows what may become of it. Someday a Chrysler may be considered an Italian vehicle.....
Sorry, I have to agree with the car show on this one. Besides, it's their show and therefore their call.