I've recently flown LHR-MIA-MVD with AA. It's not the first time I do this, but to my surprise, it was the first time I didn't have to pick up my suitcase in Miami and go through customs with it - I checked it in at Heathrow, and picked it up in the final destination.
Is this a recent policy? I'm particularly interested in knowing what will happen with my return flight (MVD-MIA-LHR). Any list of destinations or combinations where they do this?