yeah this is an excellent point.
if anyone is wondering,
these are the locations where US customs is in another country, and you 'enter' there before you board your plane:
Dublin and Shannon in Ireland; Aruba; Bermuda;; Nassau in the Bahamas; and Calgary, Toronto, Edmonton, Halifax, Montreal, Ottawa, Vancouver, Victoria, & Winnipeg in Canada.
(& Abu Dhabi, UAE, prolly not worth mentioning here but just completing the list)