Falconflyer,
"When Iberia operated a mini-hub in Miami with based DC9-30s (later MD-87s), spanish crews and EC-registered aircraft were used. What's the difference?"
I'll tell you in other way. Do you know why Iberia is not longer operating a hub in MIA? Because USA administration does not like to operate any route unless you are americans. Otherwise you will find out a lot of problems and pressure coming from your american airlines.
FEDEX is operating in Europe, let's play the same rules you do in USA with foreign companies. For sure you will complain about that.