I would guess... they don't want a class to be very strong defensively and very strong offensively at the same time. So the defensive power currently inherent in the class is preventing them from adding additional offensive powers. Maybe they feel the class needs more offense in arena, and are planning on removing some defense to make the class still balanced.

Looking at the general lack of changes to prot tanking... the old adage, no news is good news does come to mind.
Two button tanking is not that big of a deal; look at the Unholy click posted by Stealthy in the wiki. Spam button A for single target and button B for aoe targets. Then have the dps spam/click on both buttons.