>>* for bonus DC Comics content, contrast this with Ma
>>and Pa Kent, who are hugely important to Superman's story even
>>in the versions where one or both have died before the narrative
>>begins
>
>DC did give us the story that named the general trope, the practice of
>'fridging' a character. The Kents are just outliers, probably because
>in many stories they aren't actually dead, so even in ones where they
>are we all sort of know their deal anyway.

I think the Kents also have the 'advantage' in that when they are dead it tends to simply be because they are old. Something that's sad, but not a motivating tragedy.