How many people and creatures in the campaign world have access to the same healing abilities as the PC's?
In most settings the PC's are very much the exception, most creatures don't have such ready access to potions, healing spells, and other in-combat healing abilities (or really most of the abilities that PC's display).
YMMV, depending on how the campaign is set up.
I think the default assumption is that at least some magical healing is fairly normal. Healing potions are too expensive for most people, but they are common and listed as easily purchased equipment.
In any case, even in modern warfare special forces are taught to triple tap with two to the chest and one to the head.