Yes, I think you are correct. I was based out of DCA last year and frequently flew DCA-JFK-DCA. I would have to say on as many as 50% of my flights (regional jets), TSA conducted additional "random" screening at the gate. Never saw it happening on the BOS/RDU regional flights or the MIA/ORD/DFW mainline flights. Just DCA-JFK, a significant percentage of the time.