Well, I think that if you explain the system in game quickly enough, then players will catch on. Just don't expect them to be able to automatically intuit it without an explanation, because they'll likely just fall back on previous learned experience.
It's all explained, but I know most players will skip the tutorial or pay very little attention to it. That's why I'm hoping to make it as obvious as possible, aside from the fact that it helps to be able to identify when particular effects have been inflicted. I hope if blood visibly (and audibly, if it's you) drips from a character the player understands they are bleeding, that when characters cough and struggle to breathe they are bleeding internally from the torso (chest wounds suck), and that when they take a hit, hear a sickening crack and one of their body parts goes limp, they know they've been maimed.
For those same reasons, I want them to be able to see a yellow number and hear an unimpressive impact sound and realize they didn't have much impact on their target. I want them just as quickly to see an orange number, hear a more impressive impact sound and see a wound graphic (just a red patch on the victim) and figure out that their hit was more effective. And most of all, I want them to see a red number, hear a wetter, meatier impact sound, see the wound graphic and the dripping blood and realize that they just inflicted a life-threatening injury.
It's just important that they be able to tell all the things that are happening immediately, and if they skipped or paid no attention to the tutorial I want them to be able to figure it out even if they aren't willing to use the help menu.