Where are the grandparents?

[drjennyfer]

No: HPFGUIDX 36066

Hi!
I'm new here, so you've probably discussed this already (sorry!) but 
on re-reading the books, I noticed the apparent lack of grandparents 
throughout. With the exception of Neville's Gran, no grandparents
ever seem to be mentioned. (Voldemort killed his at the beginning of 
GoF but they were his father's parents and therefore muggles.) We
know that wizards live longer than Muggles, so they can't all be
dead. 
Is it merely that they are unimportant to the story/plot?

Jen