From the EDU file:

Spears have 0.6 lethality.

Swords have 1 lethality.

So think about two units, both with same stats but one armed with sword and another with a spear. Spear without "spear atribute" of course.

The sword will perform 66% better than the spear. Vs every enemy.

I don't know how much is the "spear" atribute penalization, but it looks to me redundant. Or maybe what is redundant is different lethalities for each weapon (which make "attack" stats meaningless).