/whisper, /tell, /reply. These were the tools of communication during early online gaming. Sure you also had various channels to talk in with your guild-mates, and you still do. But these days if you want to be competitive in any way, typing is just out of the question. You've got plenty of choices for when you want to get on a headset and chat. But sometimes too many choices is a bad thing. If the game you're playing has their own built-in voice chat client, then it just makes everyone's life easier. Which is exactly why Blizzard is entering the voice chat game.