No I believe it is to represent how hard it is to remain effectively offensive when you raise your fists (with no specific training in using them) and your opponent raises a sword...or 3 inch claws...or a big mouth full of pointy teeth.
And how hard it is to parry effectively (human instinct is to pull our hands away from danger not rush it toward it). Since AoO for certain actions exist because you "drop your guard" (i.e. cannot parry effectively for a moment of the round which is assumed to include a constant interplay of dodges, strikes, and parries), it makes sense that a person not trained in marital arts would have trouble being in melee combat with an armed person actually trying to hurt them.
DC