Basically, Apollo was more of a mediator between Zeus in Olympus and Perseus on Earth. He played much more of an active role.
[seeing Perseus after destroying his family]
Hades: Interesting.
Perseus: YOU!
[in a fit of anger, Perseus charges at Hades before he hurtles the soldiers at him]
Athena: [approaching as Apollo sits on Zeus's throne] Comfortable?
Apollo: What are you doing here?
Athena: Thinking... Our father is blinded by his anger. Trusting Hades with this power is a threat to all of us.
Apollo: You tell him that. Just give me some warning so I can put some distance between us.
Athena: If Hades is able to release the Kraken, it won't stop at Argos. All of humanity will fall... And then so will we.
Apollo: We can't oppose Hades.
Athena: But this Perseus is...
Apollo: [raging] NO!... How can our existence depend on him?
Athena: We'll have to do something.