I could buy your argument if people turned in an absentee ballot requested by grandpa, who then died before he could mail it. But 8-10 years after gramps dies?
In Florida, you have to request an absentee ballot and give all sorts of information. They don't just send you one year after year.
My family comes from Jackson, Tennessee, and they make them strong and opinionated there. If anyone could vote after death....
Well, who do you think cast those votes then, if not family members or other familiar people who knew those specific people were dead.
If it were thousands, it'd be significant. This number seems to me to be a fairly typical percentage of malfeasance in any human endeavor.