It's true the game CAN work without dialogue... we're just thinking that it would be more immersive in terms of storyline if Link had greater interaction with the characters rather than just (not even saying) IMPLYING "yes" or "no"
Then why say he should have a voice? :hmm:
Zelda: Please help me defeat Ganondorf!
Player: No. I'm busy.
When is anything like this ever implied?