The same thing occurs in Canada. But I believe the first person we contact upon re-entry is actually a customs officer. If they cannot determine your admissibilty to Canada, then you are sent to seen an Immigration officer. They also scribble a number/code on your customs card, and that card is collected by another officer before you leave the baggage hall. If you're the one with the lucky code, they send you over to another room to question you some more.

That's my understanding and my experience of how entry to Canada works... someone correct me if I'm wrong.