Not only it doesn't make sense, its not even like that in WC3.
AoE there had no target limit, unless you talk chain lightning type of abilities or ressurection abilities.
Damage had no caps of any sort, you stood in AoE, you got hit by it.
AOE damage, for instance - Tauren Chieftain's lvl 3 shockwave is capped at 2400 max. So basically there's a cap to how much damage it can do in one shot. AOE skills did X amount of damage to Y area regardless of how many units were in it,and WC3 approach was to limit the damage to approximately 12 units per cast.
With that cleared, of course it should be implemented differently for COH2 because :
a) WC3 is unit based and COH2 is squad-based
b) we don't want to cripple the anti-blobbing aspect of artillery,rockets, and shells in general.
Why? The objective is to reduce single squad insta-wiping, because :
a) squad wipes are not something in control of the players, thus is an highly RNG-limited situation;
b) and yet concept of vet levels in the game means squad wipes affect the game results way too much.