Not only they overpay the workers, but I'd say the other obstacle, as mentioned earlier, is that Americans won't pay much for their cars.
We'll use the Pontiac G8 as an example. The V8-powered GT model there is what, about $30,000USD? The G8's MSRP is LESS after conversion than the basic fleet pack Commodore here, with a 3.6L engine, four speed automatic, and no airconditioning (although probly 99% of cars option it).
The reason the European Fords won't come here has also been mentioned, price. I highly doubt they'd be able to bring a Mondeo to the States and have it on the showroom floor for less than $20,000USD. Maybe with a ~$25,000 pricetag and a Mercury badge, but still not that likely. We get them quite a bit cheaper than they are in Europe, IIRC. The basic Mondeo here is $30K (as is most of the Camry-class cars).
Can't expect perfection for such a low price.