For rogues, enemies come in one of three group sizes: a single enemy, two enemies at once, or several enemies at once. Subtlety rogues love to focus on a single opponent, combat rogues absolutely soar when destroying two targets, and assassination rogues are the kings of sustained damage on multiple targets. Combat's AoE damage to a group is pitiful, while subtlety rogues start falling behind the instant there's more than one target on the field.
The balance of rogue AoE today is determined by two abilities: Blade Flurry and Fan of Knives. These are currently our only two multi-target abilities, and so each spec's AoE potential revolves around these two moves. Mists of Pandaria is changing everything we know about rogue AoE by introducing a brand new AoE finisher, Crimson Tempest. In addition, the AoE hierarchy is also being shaken up via the revamping of Fan of Knives. The days of mindless FoK spam are over.