The reason why is because of the fairly loose IP policies GW has (as I read on Dakka from a company that consulted an IP solicitor). Basically GW own the IP to complete models, and to images of complete models.
They do not own the IP to every single component part, or in this case the face of an ogre.
Hence why you see companies releasing ork heads, space marine inspired shoulder pads, alternate rhino doors etc.
I like the model generally, except the hands (pointing at an awkward angle), and the head (needs a helmet). Neither of these would stop me buying it though, if I were so inclined.