At least they have a reason now.
I don't remember if it was a bug with DF or my particular install, but I'd pretty sure I remember a game where atom-smashing someone not only erased them from existence, but memories of them. Dorfs would feel bad and not quite know why.
I just checked version 0.21.93.19a (the very first DF release), and "crushed by a drawbridge" appeared in the string dump - whatever you're remembering probably didn't actually happen.
I don't mean to contradict anybody but i've smashed plenty of invaders, citizens, intelligent cavern critters etc from a easy setup and never seen a single related negative thought within the recent 47 versions all the way to the long waiting period of 44 by people they are close to. Im inclined to believe more weight behind the theory if a death reason isn't given it doesn't exist in a dwarf's mind because the game is funny about things like that and it just seems more probable that it fell through the net.
All the slabs written up for crushed invaders and other beings return as going missing, therefore you can crush people without retribution even if someone is around to report it and recieve a relative slap on the wrist for 'missing', when in reality i imagine all those goblins
ought to be furious you destroyed their troops without even fighting them.