Odd. I remember many guides and calculators including block in their definition/calculation of effective health. Seriously how often do you get stunned or have mobs walk behind you? (anub adds being a different problem here). If anything else the increase in armor is making block/blockvalue a little stronger. I hope I remember correctly but a block is factored in after mitigation through armor.
I do think the amount of missing defense on the Tier 10 chestpiece and the crafted items is quite nasty to miss out on. It's a significant amount of chance to miss, and a bit of mitigation through block (which I think is nearly neglegible because of the increased armor that's 100% effective). I'm not much good with numbers - but It'd be nice to see a total breakdown of the gearsets vs a specific preset of incoming damage.
My lack of proper signature actually is a proud minimalistic stand