Hmm. My reply is going to be a bit short, since the question is small! However, it brings up a good thought. I am glad it doesn't work.
- The thought of interacting with four other COMPLETE strangers, possibly having to mute in game sounds because of them (if muting sounds even affects that aspect) is just too much of a pain to do every single random 5 man dungeon.
- Plus, my guess is there would be some annoying players, younger players (who are either immature in what they say or immature and don't need to hear things older players may say) or speech-challenged players, two groups of which could be taken advantage of. That sweet little girl does NOT need a headset to communicate with random strangers on the internet. She really doesn't.
- Accountability. People may be rude as all hell over voice chat and not have a care in the world because they aren't on your server. At least if a random pug on your server gets in vent, for a raid, you might have an inkling of who at least a quarter of the people are. If the RL is rude, people will drop.
- I'm already chatting with my guild on vent. Why do I need to stop for a random 5 man?
So all in all, no voice chat in cross realm dungeons, mainly for reason number 3.
Aliera @ The Violet Scribe
Blacksen @ Blacksen's End
Azryu @ The Arcanery