You would have to be pretty dumb to play a subtlety rogue right now, right? If you check out World of Logs or DPS Bot, it's one of the game's worst specs. Subtlety is ranking down there with frost mages, as usual. Blizzard is buffing Sanguinary Vein by 4% in patch 5.2, which results in a slightly smaller overall buff for subtlety. Toss in a couple of extra Vanishes from baseline Preparation, and you're looking at a reasonable DPS boost for sub rogues. But how can a few percentage points of damage make up for the 50% gap that subtlety is showing on the meters?
Subtlety is not doing just 50% of assassination or combat's DPS. In fact, top subtlety rogues are parsing right up there with the best assassination and combat rogues in the game. Subtlety's problem is self-fulfilling: the rogues with the most skill and the best gear aren't playing sub because it looks bad. Subtlety looks bad because there are so few parses from rogues with the appropriate skill and gear. Most subtlety parses are from poorly played rogues in PvP gear that are just soaking up valor points and leather gear.