One of Cataclysm's biggest changes came in the form of the stat redesign. Blizzard's team made several huge changes to the stats we were used to seeing on our gear. Attack power was rolled into agility's base potency, while armor penetration was never to be seen again on an item. We picked up a new, role-agnostic stat in mastery, with the hopes that it might help consolidate gear between the various rogue specs. Finally, haste was changed to increase the resource regeneration of melee classes and specifically accelerates the rate of energy regeneration for rogues.
Haste has always boosted our energy recovery in PvE, although that mechanic was reliant on talents like Focused Attacks and Combat Potency. Now, all three specs see an energy boost from their haste, with combat still regenerating the most energy due to Combat Potency. The idea is that as your character gains gear, you get the ability to push more buttons per minute. As we progress through raiding tiers and the ilevel of our gear climbs, our rotations should be becoming more robust.