The Dodge rules makes sense against grenades, since the rules system is a discrete representation of a continuous situation, meaning you'd see the grenade coming and have a chance to create distance (since scatter isn't dependent on distance, the time needed for the grenade to land might be constant enough that you won't have to fiddle with dodge bonuses/penalties depending on the Range) before it lands.
It might be different with spells, though: while page 280 and page 283 combined can be interpreted as "non-subtle AoE spells will be noticed when they're travelling to the point of impact, and even with subtle AoE spells, you can make a test to notice them", I'm not sure if the time between the spell being sent off and the spell hitting the point of detonation is enough to justify a Dodge test.