Problems with self-healing:
-in real life, if your armor is damaged it doesn't self-heal
-serious injuries in real life (and I would consider losing 75% of your hit points to be representative of serious injuries) require medical attention... in modern day that might be a cast or drugs or something. Back in the day more likely these injuries became permanent. On that level it makes sense to me for units to not self-heal.
-anything AoM can do to discourage people from doing hit and run fighting and drag out the game is probably a good thing.
Good things about self-healing:
-in some cases, it does make sense for a person/animal to heal over time
-other games have done it with some success, even having self-healing depend on the unit... typically healing fully takes a long time which is good.
H, C, C, H, C, C, H, C, C, H, C, C