Look at it this way:
My Zons GA = 533-6,301 + Critical + Deadly + Crushing. Factor that in together and you get ALOT of damage. SO lets say you have no block and got like 800 more life by doing no block. Like 10,000 Damage Guided arrows nail your ass with no block and after PvP penalties and DR amounts your 800 life is cut down in 1-2 hits. While max block prevents 75% of those hits...its common fucking sence...get max block.