I have a sneaking suspicion of how 'don't speak ill of the dead' got started.

Perhaps you have not been exposed to as much superstition in your lives as I have, but I know for a fact that there are people who to this day believe that dead people can haunt you and can hurt you. It is only a step from that, imo, to postulate that he/she is listening to you talk. About him/her.

I've even been told that the reason that so many people die quite quickly after their spouse died is that the dead one misses them and has come for them, ergo, take care of your health, especially after someone you loved dies.

And watch those dreams! They'll usually warn you.

:)