Though that is pretty much the case returning back to the USA as well, no? I've never once had my bags looked at by customs at Dulles airport...occasionally there is a cute sniffer-dog that will roam around, but I'm not sure if they are looking for food or drugs. I imagine the "x-ray/image" screening of checked luggage at the departure airport suffices for customs.
An interesting side-note: my partner flew back from India via Dubai and said the US has a full customs/visa service in their airport, so you go through the visa/customs stuff on their side and when you land in the US you can just leave--no passport check or anything. If you've ever flown back into Dulles, this is huge as the lines for visa/passport screening are looooong and painful.