I took up middle-ages reemnactment for a hobby for a little while, the sort of fighting that you do with actual steel swords and spears, not the rubber versions used for LARP.
I was very surprised to discover that, contrary to everything I'd learned from tabletop RPG's, the key factor in combat wasn't the amount of damage the weapon could do, but its length and speed.
The best example of this is the spear. This weapon is usually glossed over in fantasy RPGs because it's not sexy enough but it's incredibly effective. A skilled spearman can use the length of his weapon to keep a sword-wielder at a distance where the sword can't be used at all, and the speed of his relatively lightweight weapon to quickly seek out weak points in their defence, before prodding in for a killing blow.
The same is true of something like a two-handed sword. It might be able to split your head in two, but a longsword is only marginally less effective at that job. The real edge you get from a two-handed weapon is the fact that you can split the head of a longsword wielder before he can even get close enough to touch you.
Fantasy RPGs are fantastic, of course, and I wouldn't expect them to offer hyper-realistic melee combat. But it made me curious: are there any systems which have rules to model genuine armed melee combat, where reach and speed are the prime factors?