I'm going to have to lean on Beckira's response for this one. Zelda isn't exactly "the greatest story ever told" and, unlike games which have voice acting (Skyrim, Fallout 3, The Old Republic, Mass Effect, Gears of War, Halo, Uncharted being a few examples), it doesn't have a compelling narrative.
As western game developers have come to dominate the industry and more and more franchises are starting to cast experience, big name actors (like Liam Neison or Mark Hammel), people have come to associate depth or quality with that trait, and, quite frankly, that's an opinion that's culturally bound and extremely premature. My opinion on voice acting in Zelda has changed quite a bit after Kid Icarus: Uprising, if only because of how brilliantly handled the script was...but, on the other hand, it's grand orchestral score was made to compliment the dialogue. The game's design was poured into a flirtatious and energetic dialogue, and the world design was meant to be as sporadic and nonsensical as the relationships and characters it created - but I digress. This is the best way I can summarize this "debate"
In general, people feel the need to be told a story, not to play one.
When people talk about voice acting in Zelda games, it usually comes with a slew of other criticisms regarding the openness of the world, the repetitiveness of dungeons and the seemingly narrow use of some items. This is when you step over the "I think the series could be better" line and into "I want Zelda to be like my favorite game" territory. The reason Zelda can get away with not having voice acting is because of the richness of nonverbal gestures and complimentary soundtrack (seriously, how many renditions of the Groose theme were there?) - and it works. Zelda isn't a game that can really benefit from voice acting, either - I (albeit personally) don't think that it adds any more richness to the world and, in some cases, you have to edit the language to make it sound like things people would actually say.
Think about the way you write a formal essay for class. Now think about giving a presentation to the class on the same subject. You're likely going to change the way you communicate simply because the way we deliver messages in text is much, much different than how we deliver them in verbal situations.
Where the idea of Ghirahim with a flambouyant voice actor tickles me heart, I don't think that Zelda needs voice acting. I'm willing to believe, though, that if Nintendo did decide to implicate such a design change - they'd do it right.
There is so much potency in the subtext of Zelda's grunts, giggles, laughs and screams that filling the spaces between dialogue is all but challenging. Those sounds, like Mutoh's scream or Batreaux's yelling contests, is really all you need to characterize their "voice". No, personally, I never want to see Zelda turn into a franchise that's marketed with big names and fancy voice actors. It's doing what it needs to do to maintain it's nostalgic value while earning some semblance of modernity.
