Well I can see using two hands with a light saber. You are still projecting weight with it. In rotj Luke was bashing the shit out of Vader with his. Two hands might be needed for balance, control and strength.
You'd think that (I know I used too, as well--it seems to make sense), but it's really not how sword fighting works when all you need is a touch to do major damage. The whole concept of really "locking blades" just doesn't happen in that case--there are parries, for sure, but if you're at all a decent swordsmen a parry is about a small deflection (To change the direction of your opponents blade) to give you an opening of attack, it's not about "blocking" it (In a way parries are more striking your opponents blade to open him up, than defense). The moment someone puts his sword up for a "power block", like you saw in RoTJ? Your opponent, if the weapon is light, is simply going to change the course of his strike mid fight and take an arm off. I forgot to mention it earlier, but someone else did--the lack of weight makes an
enormousdifference in how you fight (Which is one reason why fencing evolved as it did). I'm not good at fencing, mind you--My buddy is a C-Ranked fencer and I take some classes for fun at his gym. But even the "saber style" fencing, which is generally heavier then the other forms (And uses the blade end)? Doesn't play out with two hands and strength blocks/attacks, because "light weapons" are just easy to change course mid flight.
Jedi fighting seems to be modeled after, as someone else said, Japanese Swordsmanship or Medieval long sword use--both styles which evolved heavier weapons to deal with armor. In those fights, strength matches happened because the heavy blade required some commitment to the swing (Which was also required to do anything to armor. You really had to commit to your blow.)
But in a duel where you're using a very light weapon, and your opponent has no armor? That kind of heavy "beating" style of sword fighting doesn't happen; it's shockingly easy to flick your wrist when someone goes to block and score a point by touching them somewhere (Which, with a light saber, means they just lost a hunk of flesh at the least). And that's with a sword that still weighs a few pounds; a sword that weighs nothing and can cut your arm off through just touching it? Any big strength matches that arose would just let the quicker swordsmen take an arm or some other part you left exposed by flicking his wrist mid flight to change where he was going to hit.