You seem to fail to grasp the entire concept of the Feral Orks. Orks start off as having WS3 & BS3, it's only when they develop into a larger community (border Codex: Orks, Orks) that they become more accustomed to beating the crap out of someone rather than shooting them. Now if you apply that to Wildboyz, who have just been found wandering the 'wild' they aren't developed enough to have a WS4 BS2.