I've never understood the paranoia about unattended bags. If you are worried about a bomb, just watching the nightly news shows that terrorists are quite willing to kill themselves in the process of blowing up others. That makes every bag, attended or not, potentially a bomb. Even if they don't want to kill themselves, why not just toss your backpack bomb to the bottom of an escalator with a 30 second delay and run the other direction?

The only point of the announcements, IMO, is to keep up the level of paranoia and prove TSA is there "for your safety", so please give us more tax money.