Originally Posted by
Mace
yes, but they can change, or rather we find out the orcs change by the arrival of the dimesnional ship in nagrand, this could have altered them enough for that to happen.
or because most life forms are titan seeded anyway they is some measure of cross compatibility
another reason could be Azeroth is able to do things lilke that make a new being from two unrelated one, somethigng that would not be possible on an intert world or without external titan/keeper or magical intereference.