Simple law of averages, with a pinch of coincidence thrown in. They were all around the 70 mark (i.e. the biblical three score years and ten).
It seems that periodically Mother Nature evens out the balance to compensate for mankind keeping a small percentage living longer.
Earlier this evening I heard that an old friend's mother-in-law died this morning and his father is expected to check out imminently; coincidence is a strange thing.