I dont think he is "that" fast, I think that it is a combination of his accuracy, volume, speed and power. The fact he can throw hurtful punches fast means that people get worried about throwing first because he can beat you to the punch, with hurtful shots.
Hatton may be a face first brawler, but he's not a slow man by any means. His punches are prety quick and sharp and his feet are damn fast as well.. that's reason he was able to track down and close the gap between himself and speedy fighters such as Malignaggi and Mayweather.
I'm more impress with pac's foot speed than his hand speed... he gets away from trouble quick and darts in for an attack just as fast.