I am thinking the longevity of the posts set in stones has to do with moisture. I have found old (date set unknown) red cedar boundary corner posts that were almost completely gone above ground but still solid in the hole. They were scribed with owner name and lot # ....which to my knowledge no one does anymore. Packing rocks around the post allows the water to drain away.
So if we make the sills and posts out of rock we should be fine....oh wait, we would have to be masons to do that wouldn't we?

Bob