On the forums at Dragonsfoot I argued that a D&D character with an ability score of 3 was simply at the low end of ‘normal’. The corollary of this is that scores of 18 do not represent superhuman capabilities. Others took a much more stretched view of the 3d6 ability score curve, arguing, for example, that INT 3 represented an intellectual disability and INT 18 genius.
Scores of 3 and 18 turn up on 1 in every 216 rolls of 3d6. If everyone rolls 3d6 in order, that’s at least one genius in every village (and one villager that is superhumanly wise, superhumanly dextrous, etc.). So INT 18 is not the equivalent to Einstein, but to the guy with the [capacity to get a] first class degree in Physics.
But perhaps everyone in the village is not rolling 3d6 in order, and so 18s are not as common as 1 in 216 in the general population. In fact, I agree. We roll 3d6 to determine the ability scores of adventurers. In fact, I do not think most NPCs in D&D [should] have ability scores. If 3d6 is the way that we generate the ability scores of adventurers, an ability score of 3 is the ability score of a viable adventurer. An adventurer with a negative modifier when resolving actions related to that ability, but an adventurer all the same. But whatever a score of 3 represents, it does not represent a disability – ability score generation is not a roll on a critical hit chart; not even Warhammer Fantasy Roleplay is that cruel and grim.