Star Wars Saga Edition area-effect attacks (such as grenades, or an autofire weapon) use an attack roll vs. Reflex Defense. You apply full damage to those who your attack roll hits, and half damage to those you miss (unless they have Evasion).
However, the SWSE errata modifies these basic rules, requiring you to roll at least a 10 on your attack roll in order to affect anyone at all, and adding the rule that, while a natural 20 is considered a hit against all targets, it is not a critical hit.
SWSE also allows an autofire attack to be converted to a single-target 'burst' attack with an appropriate feat or talent. A burst attack doesn't take the penalty to attack that normal autofire does, deals no damage on a miss, and can critical on a natural 20.
I would guess that the rules currently being used for Fireball attacks in 4e are either equivalent to the pre-errata SWSE area-effect rules, or else include some equivalent of 'burst-fire' mode, allowing an area effect to be focused exclusively on a single target, probably with enhanced effect on that target.