Venom initially effected all robots but it very quickly became apparent that it was utterly useless as a weapon when it effected friends and enemies alike.
Besdies, species being immune to their own venom is hardly a new idea.
Th Komodo Dragon has such a weapon. It is actually more a concoction of deadly bacteria than true venom but the concept remains the same. A dragon is immune to venom from another dragon.
Likewise the different animals (of the same species) that make up many jelly fishes such as the portugese man-o-war, are imune to the stings of other nematocysts in the same, and other, comunal structures.
Sea slugs are not only immune to poison and venom from others of their own species (and often other species too), but they use the venom that they ingest to defend themselves.
The same is true all over the animal kindom so why should DB be any different?
Anyway, was the question, how to actually use venom in DB or was it just simply a comment about un/realisticness of it. (I think that may be a completely new word :D )