So I used to do LARPing (think of it as live action D&D) every month. We used very light PVC/foam weapons to fight with
. I used dual wield swords, mostly for the versatility of them. I could use one up and one down for more defense, or both up for more offence (there were a lot of people who used sword and shield, but that doesn't apply here). There were hundreds of us who played and we had tournaments every year. No one ever used a Bo Staff (double bladed light saber) because they were an easy target. And no one ever used a single sword. I won my divisions tourney a couple of times using two swords. Every time someone swung at me high, you block with one sword and swing at the legs with the other.
There is a lot of theory in this thread, but I can say from experience. Two swords are better than one, and better than a staff.
With all due respect, I don't see LARP'ing being full of very credible swordsmen; martial, sport, or otherwise. Most LARP's i've seen, while fun, are a lot more randon and chaotic because it's just a lot of people, most with no experience wielding a weapon, just having fun. There's nothing wrong with that, but it does not make for impressive swordsmanship.
A single sword is, generally, more of a proper weapon than wielding two swords; and in battlefield situations like the ones LARPs imitate sword/shield should always come out ontop, but only if people are properly practiced. You don't swing high/low generally, you strike for center mass, generally from just below the neckline and down towards the hip.
When you're in sort of a lowbie area of skill, like in a LARP, two swords probably work because people aren't trained for proper weapon control and how to handle the chaotic, and likely consistent offensive two swords would offer. I think if you flooded a LARP with, say, ARMA students or some such you wouldn't see anybody using two weapons.
That said, of the PVC weapons i've held, they're often too uncomfortable and unwieldy for proper technique. I am sure that isn't always the case though...