Rogues have an identity problem. We're a class that's based around Stealth and subterfuge, but WoW's combat mechanics aren't conducive to that design. Our opener abilities are immensely powerful to compensate for their relative unavailability. If you've ever dueled another rogue, you know how critical the element of surprise is to PvP combat. A rogue stuck in the open is hardly a rogue at all.
The flip side of that coin is that a rogue in Stealth is a powerful force. Cheap Shot and Garrote are amazing abilities without any true cooldowns, and Shadow Dance keeps subtlety at the top of the arena charts. Rogues that specialize in PvP are focused on how to sneak as many openers as possible into an encounter. Vanish, an inconsequential PvE ability, is one of the most potent offensive PvP cooldowns available. The divide between a stealthed rogue and an exposed rogue is massive.