Oh wait, I think I got it. You see, the body can only defend against organisms and foreign organic molecules that are harmful to it, but it has no immune response to simple chemicals. Food poisoning is almost always bacterial or viral in nature, which means the body can mount an immune response to it. The immune system signals the brain via the gut nervous system that something is wrong, and the brain recalls what it tasted or smelled most recently, and tells you "Don't eat that." Regardless of whether it's usually poisonous or not; the brain nor the body makes that distinction.
This doesn't work for alcohol, because there's no immune response to it. Instead, alcohol goes directly from the stomach into the blood, and to the brain, where it starts wrecking shit, and then the brain induces nausea because it, and not the body, is sick. Which is why it doesn't create a lasting negative association: it's not using the proper pathways. Sneaky bastard, that alcohol.
