Dude, regardless of whether or not you need strength to increase lightsaber damage as a Sage/Sorc, the fact of the matter is you shouldn't be running up to melee range as a Sage/Sorc. Lightsabers for them are basically for defensive purposes and all of a Sage/Sorc abilities rely on the Force. If you don't like it, reroll to a Shadow/Sin/Knight/Warrior.
As for your previous comment on how an Operative has their weapon damage increased by Cunning, it's because unlike a Sorc/Sage they are SUPPOSED to use their weapon for DPS. They don't have Force Powers to fling across the battlefield.
You really need to stop caring about Lightsaber damage as a pure Force casting class, because it makes no sense.