Well, yeah, you need to be able to see the lasers in the movies, so they make the pretty little bolts you see. In actuality, lasers are light: Light Amplification by Stimulated Emission of Radiation (LASER). Therefore, the laser 'bolts' would move at the speed of light. It is possible that the light is slowed when it passes through focusing crystals, I suppose (or is that the Tibanna gas's job? Anyone know?), but it would still be moving at relativistic speeds. There is no way ANY projectile could ever reach relativistic speeds; gunfire comes nowhere close. So therefore, the lasers really are faster. But how entertaining would it be to see a firefight with nothing being fired? You gotta have something to show.
Also, the mess is always what I attribute to laser superiority. When you use bullets, you get nasty blood and gore all over the place. Blaster technology, all it messes up is the corpse. As the dawn of the Old Republic was supposed to be the start of a more civilized age, it makes sense that they use more civilized weapons.
Now that blasters are so well established galaxy-wide, it doesn't make sense to use slugthrowers. Resupplying becomes a major issue at some point, and power packs are far more universally purchasable than metal slugs. And dealing with a single power pack rather than dozens of tiny shells? Laser technology is superior in just about every way when you think about that.
GPI: Fondly regard crustacean