Originally Posted by
catandmouse
This was true until ESTA. With ESTA you get no I94s anymore, so nothing to surrender when you leave the country.
Actually, what I posted remained true even after ESTA became a standard requirement for US VWP entries.
It is only within more recent weeks that USVWP passengers have been told filling out the I-94s is no longer a general requirement, and even then the exit controls of the sort I mentioned are still in play.
For years now, the passport details of passengers departing the US on flights has been used by DHS as part of US exit passport control. That remains the case, ESTA-user, US citizen or otherwise.