Future of Tank Balance in Cataclysm

It seems that the game design team intend to keep the four tanking classes individually unique, rather than only superficially different:

"Rather than have all the tanks have the same health, armor, avoidance and cooldowns, we’d rather have four unique tanking classes rather than just superficial or artistic differences. Yes, that design is harder to balance, but we think class distinction is ultimately more interesting, which is better for the long term health of the game. The goal remains to have all four tanks be viable for any encounter, assuming sufficient gear and skill, and any differences in performance on individual encounters to be minor."

Any encounter? I wonder if that includes 25-man hard modes.