It seems like a small change, but it could be the herald of something larger. It's a change to the way the defense skill is described in-game in patch 2.4, as reported by World of Raids. I'll let them describe it:

* Old value: Higher defense makes you harder to hit and makes monsters less likely to land a crushing blow.

* New value: Higher defense improves your chance to dodge, parry, and block attacks, makes you harder to hit, and makes monsters less likely to land a critical strike against you.

So what does this mean? They've added things that have always been part of the skill, but have not been explicitly mentioned on the defense tab before, but what's most intriguing is what they've taken away.

I'll explain after the jump.

The new description has no reference to crushing blows. One of the biggest ways a Paladin or Warrior knows they're ready for the big time in tanking is if they can completely remove the chance to be crushed by an enemy using gear, talents, and skills. One of the biggest complaints that Feral Druids have had is that they have no skill or talent (such as Shield Block or Holy Shield) to help them avoid crushing blows. It's a topic that's on the mind of every serious tank every time they go to any raid instance.

We already know that the game developers want to get of crushing blows, thanks to an IRC chat with Kalgan and Tigole hosted by Stratics (Which we at WoW Insider liveblogged here, with the full transcript mirrored here at World of Raids, if you never saw it). We know as well that they seem to have already started to play around with the idea, as recently implemented bosses such as Halazzi of Zul'Aman often do not use crushing blows at all. While they cautioned in the aforementioned interview that any real action on crushing blows won't come soon, the removal of the mention of crushing blows from the defense skill may indicate that it's still on their minds. I'll most definitely be interested to see if any of the Sunwell bosses still employ the mechanic.

Personally, I'd say the best money is on them waiting until WoTLK to completely do away with crushing blows. Level 80 should allow them to more easily balance out the four tank classes while taking the removal of what has been a rather dominant mechanic in many encounters up until this point into account. That said, it could still be starting now, with this seemingly innocuous change becoming the harbinger of a much larger change in the way we tank.