I would agree with the posts above about all not being as it seems. The green channel may look unmanned but you can be assured that there are teams of people standing behind the two way mirrors and watching all the CCTV footage. Even better, I have certainly seen what I take to be plan clothes customs officers observing people in the queue for their passport check and while waiting for bags to show up on the belt. I think this is actually quite an intelligent approach - you will learn much more about someone's intentions if they think they are not being watched, or from how easily they recognise their bags, or how they react when handling the bags.
I have noticed US airports moving in this direction too. Of course they still have the officers collecting forms, but I have seen places like IAD installing quite prominent-looking observation posts in baggage reclaim.