Asking it to make sense is ridiculous. I've parried the Oppressor's landing damage from across the room before. You can parry Earthshaker in t13. SCH and SMN can parry, albeit rarely, with fucking books. Its never gonna be logical. What's more is that parry and block still allow 70-80% of the damage through meaning if it was a real life parry or block, your character did a really crappy job.

Mechanics like this are fun to chit chat about with friends in game for sure. Threads about them on the official forums are kinda like... "they're never actually going to do this... why is this here..."

=/