Mob/Entity Griefing in Survival 1

I've noticed in the Survival Servers, the Wither can destroy blocks in the overworld. I do not know if they can affect claimed area as well but they can destroy blocks around them. Anyone's home can be griefed by spawning a wither in or near their home and can either destroy the blocks, spawn kill players, or even both. As for TNT does damage to entities, it does not affect the terrain. Unlike TNT, Beds, which explode in the nether or end when used, can destroy blocks, which can be bad if this is used by tp killers. Hopefully this gets fixed soon.