I can't see how this change is going to be removing the caps. It feels like we're going back to the old model of pushing crushing blows off of the attack table, except now the goal is to push normal hits off of the attack table.

If you can guarantee that any melee hit done to you is reduced by 30-40%, if it even makes contact, getting to that point would push the value of mastery way above any other stat, including stamina.

I think the changes Blizzard is trying to make right now to prevent block capping are a good start, but like Aix said above, it just looks like they're delaying it by a raid tier. In order to prevent this from causing major issues later in Cataclysm, they're going to have to prevent end-game tanks from reaching that point in their tier 13 gear. The only way I can see this happening without a huge overhaul to the mastery is by adding diminishing returns based on your overall avoidance. I don't really like that solution, so here's hoping that the designers can come up with a better solution.

This is what the solution will be at the end of the expansion, betcha.

"Breath of the Dragon: The blazing presence of Deathwing's lair reduces the chance of an enemy to block melee attacks by 20%."