Avoidance is avoidance, even if you must surmount diminishing returns and chill of the throne. Pure stamina stacking is only effective up to a point, especially since the intent is to have bosses that will be connecting more often for far less.
i will say that most tanks will still be gemming for stam in ICC. i know i will be. there is no reason to gem for parry as the 20% dodge reduction is done AFTER diminishing returns, so u would still get more out of dodge (unless u have a ratio of dodge: parry of 1.875:1, then gem for parry) but dodge will still be greater than parry.
i doubt the dodge reduction will really be noticable anyways, and if bosses arent hitting like trucks(which is blizzard's plan to smooth out incoming tank damage) then stam will become even better to gem for