I would love to 100% agree with you on that part but that did turn out to not be the case (hence what Kynox, Cypher and i discovered a few month back), but ye generally they do have their shit together on that part.
Ahhh damn, you were too fast.
We managed to hack into the Wrath of the Lich King Friends and Family alpha by packet spoofing.
We managed to allow change of area trigger offsets by packet spoofing
and we managed to do name change by packet spoofing. (well not directly packet spoofing but rather editing something that would cause the packets to change)