This is true of most "security" measures that have been put into effect in recent years. Security checks at Disney are a perfect example. Only making every 7th or 8th person go through a metal detector is a farce. As Ryno said on the show, they should be screening every single person equally. Bag checks are the same. We've encountered everything from a quick glance to the guard taking out every item and checking inside every bag and container. And we were just at Disney last week when the temperatures were in the 30s and 40s. People were wearing long heavy winter coats with plenty of pockets and space to hide things but nothing special was done to screen them. I could very easily have been concealing something.
Most security serves two purposes. One, it gives the public a sense of security (John actually used that phrase on the show) and two, it gives the security crew time to watch people and look for shady behavior, someone who looks nervous, perhaps someone wearing that long winter coat when the temp isn't that cold, etc. And th ere definitely is value in both of those things but it's far from a perfect system.