Are we including the ones that were put out of businesss by others just moving there to put those already mentioned out of business, and those just offering services to crush competition before pulling out?
There is no reason why STN can't support USA routes. In the past start ups have been ihindeted by flag carriers moving in at a loss just to put them out if business.
That was in the era of BAA of course, now the airport is independant if the other London airports things might be different.