Indeed Canada, Ireland, and Abu Dhabi wait until you arrive there from the USA to do their own immigration so it only goes one way.
The US-Canada agreement is the oldest one, largely due to the amount of cross-border air travel, and Canada has the right under the agreement to operate preclearance stations for the Canadian border inside US airports, but has never chosen to do so.
Saves a lot of time and hassle.
http://onemileatatime.boardingarea.com/2014/09/07/etihads-ab...
What sounds really, really annoying is that there are no facilities whatsoever (save for a coffee kiosk) and that you can't even sit down until the gate opens.
Personally, I wouldn't know since I never flew via Abu Dhabi (let alone to the US).
(he ate too much dangerously delicious lasagna when in Malmo)