Wes Welker is small, and not particularly great at catching throws far from his body. What makes him a great receiver is that he's elite -- probably all-time elite -- at using his legs and brains to move his small target area well away from defenders. And he is also elite at running elusively after the catch. Welker's target area isn't super-small, as is evidenced by the fact that Matt Cassell was able to feast on it much as Brady does. But it is small enough that defenses can indeed sometimes hamper his success -- just as they can for every other receiver in the game.