Isn't this just a tacit admission by the TSA that their normal screening is so far from perfect that it lets plenty of stuff through?

Even with gate screening, I know for a fact that the TSA misses quite a bit of stuff. The best man at my wedding flew with a 6" folding knife in his laptop bag and went through two hand searches at the gate during his trips; the knife HE found when he returned home and unpacked--no one at the checkpoint nor at the gate hand-search caught it.

Meanwhile, the TSA is focused on confiscating lip balm and sunscreen while the terrorists are slipping right past them.