It's not for no reason though. They have already said they don't like the unintended consequences of buffing the bombs, and that it was just a temporary fix.I fully expect that this will happen. I also believe Frost and Arcane will be compensated elsewhere.
I think they want Arcane to actually be the turret option with RoP being the optimal talent. I expect that with a bomb nerf, that single target will be buffed by a fair amount to make up for the heavy movement we see in SoO. Do crap dps while moving, do exceptional dps while planted after the ramp up. The new tier set bonus reinforces that idea.
As for Frost, we have already speculated that the change to Mastery was to make the spec less bursty in PvP while paving the way for a PvE buff. Removing the ramp-up of Frostbolt and buffing Mastery would do a lot for Frost PvE.
As for Scorch, they can very easily nerf that too.