Originally Posted by GUWonder

It is indeed a form of exit control, and no less so given that DHS is supplied with actual passenger manifests from the airlines and also has the listing of passport details collected and filed for the departing passengers on the passenger manifest of the internationally-departed flight.

When it comes to flights on common carriers, US exit controls of a sort are in place, and part of those controls include DHS employees interrogating departing US citizens as part of fishing expeditions when and where DHS deems it appropriate; other part of those controls are as I mentioned above.