Ok finally my membership was approved. I have to point one thing out some poisons work through epithelial linings thats probably the kind of poison rouges put on their weapons. Proof of this is maces can be poisoned they don't cut so wouldn't be able to get the poison into the blood stream. yea I'm not nitpicking I'm just saying. Thats also why the poison still works on undead.
Well, basically, Maces don't cut you, but they bash in your skull or any other body parts instead. I'd imagine that your body would start to blood too, eventually. And this, the poison gets in your target's body.
Blizzard just merely fastened this progress.