Honestly (and as a business, I understand it), they set the film throughout the world to appeal to a worldwide audience. While Cars did amazing business in the US, it wasn't quite as successful overseas.
To quote Yogart from Spaceballs, "moichendizing!"
I know it will drive purists nuts, but merchandise sales are the only reason there's a Cars 2.
Btw, I just came from seeing it and it's fair at best. Almost as though Pixar didn't actualy make it. Definitely their worst film and a shadow of the original. The story absolutely stinks. It'll have much more repeat viewing once it's on DVD in our house than movies like Wall-e, Up or Ratitouille, but that doesn't mean it's good.