Quote fromQuote fromY'know, land-claim flags would fix or alleviate most of those problems.
Land claim flags, as far as I know, were never meant to provide building protection. All that I've heard Notch say they'll do is keep monsters from spawning or disappearing.
Look harder, then. It says quite clearly that they'll prevent other players from building in that area, and from this we can assume that it will prevent them from destroying too, since otherwise it would make no sense.