My guess is that the demon lords use their influence over the world to ensure that diseases are always painfully lethal. It strikes me as something they'd focus on. :b Deal.
Imagine a world where treating a disease involves leeches then wonder why disease is in it's current form.
Historically; disease killed far more people than any war did and very few if any could be stopped from running their natural course.
Even today in our modern health-conscious society we still have had recently (In history) things like Small Pox, Mlaria and others that tear through the undeveloped nations nearly unchecked.
Actually, smallpox is not uniformly fatal. Neither was bubonic plague. I would like to agree with the folks who think there should be some chance of recovery even without the use of artifacts or healing spells.
It doesn't really bug me that there isn't, though. Because all sides must abide by the same rules. It just seems like another example of bad things outweighing good things as was the case with luck. And that decay spell.
Most diseases would be over in a month. Either your'e dead or your'e alive. The diseases of dominons are more like leprosy or other wasting diseases. Your body festers and bodyparts fall off. Sometimes you loose an eye, sometimes you loose your mind and sometimes you loose your chest