[ringmaster]

The airlocks are not at all of the terminals, so it's not surprising you didn't see it.

Here's a PDF explaining the airlock rooms at PHL (they call it a "secure exit lane system") with photos: http://www.aci-na.org/sites/default/files/tufts.pdf

If you look closely at the metal turnstiles in the bottom-right photo on page 8, you can see that there are glass doors between them. These separate and close by sensor to allow only one person at a time through the exit passage. This room is, by necessity, fully covered in cameras, and as other posters have said, it's a short jump from this into something with software recognition that locks the doors and waits for the armored men with clubs.

Sure, it's a far cry from the firetraps that those glass tubes in Syracuse are, but this method of containment is not new -- we were just not really paying attention to it before.