RE: Dublin US pre-clearance facility:
I was just enjoying a conversation over coffee and a donut with a management employee of the USCBPA. I was asking about the pre-clearance of airline passengers at foreign departure points. She told me that it is the airline(s) who pay for this service and, it is, for the most part, regular scheduled carriers with extensive interline or code sharing agreements and many onward travelling passengers who benefit the most from the procedure. They (airlines) schedule closer arrival and departure times, due to the pre-clearance of connecting of both passengers and their baggage. Charter type passengers wouldn't benefit much from the system and, the airlines they use wouldn't want to pay the extra fee for giving their customers this extra service.
The cost doesn't just entail the USCBPA having an area at an airport but also their accommodation in the foreign country and, believe it or not, the salary of the agents + out of pocket expenses for same and all re-location costs. The US government will accommodate most requests for "off-shore" clearance but, won't pay for it.