As a pax I was always under the impression that this was an everyday occurance and that the "rule" of no accompanied bags was just another attempt to reassure the less well informed public. I could list possibly 12 or more occasions when my bags have travelled on a different aircraft than me - usually when they've been "left behind" and arrive a few hours later but twice, both in the US, when they've actually arrived before me
on an earlier flight (where I'd allowed extra connecting time, which obviously wasn't needed). Yep, I know that it'd be hard for someone with ulterior motives to actually plan this, but still makes you think!
Maybe it's just accepted as a fact these days that the 'bad guys' really don't give a toss if they go down in flames with the aircraft.