I too would be devestated if circumstances meant I could no longer see my grandchildren and I do think that grandparents should have rights to see them, depending on how much input they have had into their life beforehand.
Sadly I would guess that most cases are because of marriage break ups and relationship breakdowns and I would also hazzard a guess that it will mostly be the paternal grandparents that lose contact the most.
I have helped bring up my grandchildren from birth. I have nurtured them, loved them, attended hospital appointments, doctors, dentists with them.Cuddled them when they are poorly and comforted them when they are sad. They spend two/three days a week at my house every week virtually without fail and I could not imagine the effect on them not being able to see me as well as vice versa. How cruel would that be? Imagine being my eldest GD who is 8. I know I am an important person in her life and have been since birth. How would she feel if suddently she was told she would never see me again? I am not being big headed or blowing my own trumpet at all, I just know that my grandchildren need me as I needed my grandma (and still do to some extent) and that their life is better with me in it.