This makes perfect sense: sociopaths are skillful at manipulation, and part of manipulation is influencing people with your looks. It stands to reason that they would put more effort into enhancing their appearance, something normal people might be too embarrassed to do.
It also fits in with another thing I've noticed: that sociopaths are far more likely to have plastic surgery. (Think of it as another "mask" the sociopath wears.) And if they're male, they're far more likely to use steroids.
Most (certainly not all) non-sociopaths are too embarrassed to have plastic surgery because of what it says about their vanity. And most guys wouldn't take steroids because it would be cheating (at least in a sports context).
Sociopaths don't feel embarrassment, and they don't feel guilt, so they do both of those things. And if they don't hesitate to get plastic surgery or take steroids, they're certainly not going to think twice about using dress, makeup, and hairstyling to achieve their goals.