A piece of steel that is only held at one point is really really hard to break - even a piece of wood is. Your argument should be that the static block displayed in Warband wouldn't help much to stop a heavier weapon, leading to a crush through and probably damaging the wrist of the defender. But the weapons itself, especially short and thus sturdy ones like the broad short sword would most likely not break into two.
We have to imagine the blocks more like parries that deflect instead of taking the force of the blow head on. With that even lighter weapons that would otherwise be knocked away in the momentum exchange can be used to defend. Read the article Shik provided.
Lastly, I doubt you understand physics at all.