They used to do that at BWI, as well, but they seemed to have stopped by late 2010. I almost understood the reasoning - the TDC was originally there merely to make sure that only ticketed passengers (or those with gate passes) could pass through security, and the TDC was originally placed farther from the WTMD than they are today, leaving enough roped queue area that, in a very crowded situation, people could have possibly slipped into the line past the TDC. Of course, the solution would have been simple - move the TDC closer to the WTMD. But BWI decided that they'd back up the TDC by having the WTMD operator check your BP as you entered the portal. It wasn't a terribly big hassle and actually did act as a "layer" to plug a potential hole in the previous layer, which was about 40-50' away.

Today, the TDCs are simply a lot closer to the WTMD, and the barriers between the landside and the checkpoint are a bit more robust, making it highly unlikely that anyone could slip into the line past the TDC, so the WTMD/AIT operators no longer want to see your BP.