I tend to agree with Martel on all points (except his decision to quote GURPS :).
From a more ideological point of view on the weapons, however, think of the juxtaposition of sword and axe, especially in history, myth, and story.
The armies of the Dark are blunt, enormous forces that through absolute brute force pummel an enemy until its dead. The scant, tiny groups and squads of surviving military of the LIght, however, operate under pin-point attacks, hit-and-run tactics, assasination, and other such delicate, precise woundings, more interested to make the enemy bleed to death from paper cuts rather than lose limbs or get crushed.
The sword and axe are analogous to this. Take fencing, for example, which is the best example of what a sword can do when it is at the extreme end of the spectrum. The pin-point, delicate blades of the rapier, sabre, etcetera, are for making tiny stab wounds or lascerations, not for hacking limbs. A longsword is less like this, but it still requires a good deal of experience and training to use effectively, unlike an axe for an undead Thrall.
A correlation to the pin-point idea can also be like the Roman Legionary and the Gallic Barbarian, as Martel pointed out. The Legionary has the gladius shortsword which is meant as a simple stabbing weapon, meant for precision, preferably through the heart. The Gaul, however, depends on hacking off an arm or two, or mb even a leg, when he attacks. A modern example might be Hitler's blunt assault on Russia (those were armies of Darkness too :). Had Hitler been more devious, or articulate in his plans and taken the Middle East first, he could have gotten enormous oil reserves so that he could either fuel a more powerful blunt assault or, better yet, divide Russia at the Urals and conquer less wastefully.
In a very poignant story which portrays a lot of good and evil, take Shakespeare's Richard III. King Richard III was a hunchback because he had trained since his youth to wield an axe in battle; so, after using only one side for such a long time, his body became deformed in its musculature and bone structure. Richard III was also horribly evil, so his use of the axe helps to characterize both as being or malificent.
Ultimately, the articulate, dare-I-say creative side, the Light, which used a more riteous form of war was the victor, despite all odds. There are many other analogies that one can derive from the units and weapons in the game that support this, but the primary example seems to be sword and axe.
