Curious as to why you think that is the option. If a fireball rolls for an attack, why would a miss = half damage, a hit = full damage, and a crit = extra damage? Even if you are coming from 3e rule-set, there are 3 options: Evasion = no damage, ref save = half damage, failed save is full damage. It would seem more logical to allow for those same 3 options and allow for everyone to not be hit or everyone to take crit damage. A fireball can be aimed so poorly that even the slow, plodding bullette (generally easily hit by such a thing since it cannot get out of the way) is missed entirely.
Of course, there could be some caster ability that states "even when a spell misses, it does X damage." I recall from a pod cast (I think) that someone mentioned thier Barbarian could (or would eventually) to do some small amount of damage even when their attack missed. But I would assume that, at it's base, a miss is a miss and does no damage, whether it be a sword or a fireball that missed.
If there was an Evasion ability, it would seem more fit to have a hit do half damage from evasion (more similar to Imp Evasion).