Originally Posted by
Melissia
That's actually contradicted by later fluff.
Dark Heresy, however, has a better explanation; in the hands of an Ork, an Ork weapon is reliable (like a lasgun is reliable, or a good quality bolter is reliable, or a revolver is reliable-- weapons that almost never jam). In the hands of a non-Ork, it's unreliable, but it's still able to be used... it just jams more than it should. I know Ciaphas Cain used an Ork Trukk, and Marines have used Ork Shootaz before, as well.
Basically, Ork technology, except for the crazier things such as teleporters and such, CAN work on its own. It just works better with an Ork using it, both because half the time only an Ork truly understands the nature of the weapon and how it should be used, and because of the innate gestalt psychic fields they emit as part of their orkyness.