An old friend's grandfather lived till his late eighties, active bright and happy. The family had Sunday dinner together; he ate well, pushed back, said "that was good"...and slumped dead as a doornail in his chair. A little funny, a little startling for the family, but I wouldn't consider it the least bit "cruel".
   But, before I hit the "submit" here, yes I know that death can come with too much pain, and it's often very sad, too often devastating, for the survivors.