But Toyota, Nissan and Honda all build substantial numbers of cars in the USA. Ford and GM build a lot of cars overseas, and even market them as American cars. Chevy's small cars are made in Korea. The new Pontian GTO is made in Austrailia. So nameplates are not a good way to measure where a car is built.
Ownership of a company is also somewhat problematical. The Dodge boys are part of Mercedes, so if you go by corporate-ism they aren't really American anymore. On the other hand Ford owns Mazda and Volvo --- will you buy them proudly?
Of course the real owners of all public companies are the shareholders. Unless you've done a lot of analysis it is probably hard to know what the nationality of the majority of shareholders of a publicly held company is.