[Kromm]

The very idea of armor divisors hadn't been invented when melee-weapon damages were first eyeballed, with the implication that the game's original damage model was relatively insensitive to penetration. It would be kind to say that damage adds approximate both penetration and wounding effects . . . really, they're primarily measures of wounding. Right or wrong, that's the choice SJ went with in GURPS First Edition (in fact, in Man to Man), and we've stuck with it ever since.

As a result of this model, the wider the blade, the bigger the damage add for being impaled by it: a skinny 1-cm-wide fencing blade or an awl-like javelin does thrust+1, a fatter sword blade up to around 2 cm wide is thrust+2, a 4-cm-wide greatsword or a spear gets thrust+3, and the broadest boar spears and the like ("heavy spear") are thrust+4. Realistically, thicker blades would be better handled with fixed damage, progressively worse armor divisors, but correspondingly better wounding modifiers. However, that isn't the current GURPS model for thrust impaling damage.

You could revisit this. If you did, you would have to revisit all melee weapons – thrust and swung, blunt and sharp – and grade armor divisors and wounding more finely. That would be an edition-level change, and one that pulls away from the current industry trend toward simplification, so I wouldn't bet on seeing it happen "officially."