Why? As he explains in the Q&A session after the talk, two frames of latency at 30Hz (2 x ~33ms) is still more than 3 frames latency at 60Hz (3 x ~16ms). You will always have at least 2 frames latency if you split the game logic and render stages like they did for TLoU on PS3, so in fact their PS4 engine has better framerate and latency.