ya when it attack(the broodlord) do 20 damage(more if upgraded) each time to the target, and the ammo is broodlings, those broodlings deal additional damage until it get destroyed or expired, so basically it do more than just 20 damage(unless they got killed instantly).
So the broodlord is a very powerful unit, it create broodlings every attack, it deal damage 1st upon landing and while those broodlings flying to the target they are invulnerable, then the broodlings do extra damage. and your enemy will have to spend time killing those broodlings, keeping them busy, your broodlord can survive much longer.

This post has been edited by narf03: Sep 6 2010, 05:31 PM

should only consider using it in multiplayer if your enemy seal themselves in, turret/cannon the entire base, do not use it on experienced player, they are too late, slow moving, expensive and cant vs air, but its extremely good against thor !!

broodlords do full damage to thor, plus they create broodlings, thor do half damage to broodlords, due to broodlord consider as armored unit, and in a fair fight, ie 3 broodlords vs 3 thors(1v1 or 2v2), broodlords will always win with outstanding result, only with 1 exception, many broodlords vs many thors and all broodlords are stack together, cause thor can do area damage, if they split out, broodlords will win. default damage for thor vs broodlord should be 6 minus off the armor of broodlord, which left 5 per attack, and broodlord do 20 minus off armor which means 19 per attack plus broodlings. if broodlings didnt get killed(concentrate fire on broodlords), they can do like 10-12 extra attack b4 it dies which is 4(?) damage per attack.

like what i said, in a fair fight =P, i think he did lose quite a number of scv 2 killed by broodlings ?