I don't understand either. I see this more frequently lately, that (informative, on topic) posts are randomly killed. It's not like the poster was a negative-karma user, either. Who decides which posts get killed?
Often it's because a user accidentally double-posts, the second post gets auto-killed, the user can't see their own dead posts, and they delete the live one rather than the dead one (because they can't tell which is which).
Clearly, to keep the balance in the system, if there is auto-kill, there must be auto-unkill also :D
bbatsell hit this correctly. I saw two replies appear and immediately killed one. It surprises me to see replies on the dead one, there were no replies when I did the kill.