I don't know if Thompson has heard yet that voice is going to be builtin to WoW very soon now, but it's true: voice is about to play a much bigger part in our game. And it's also true that voice changes things a lot-- in my regular guild, I will often jump on our Teamspeak server just to chat with my fellow guildies and friends, even if I'm not in a group. In It came from the Blog (the official WoW Insider guild in which I occasionally can be seen saying crazy things), we haven't set up a Vent server (although it's coming, guys), and so I had the strange experience the other day of running an instance with only text chat to keep me company. Don't get me wrong, I like all the guys in IcftB, but I don't know if the reason I don't know them better is just because I haven't been with the guild as long, or if I just haven't actually heard their voices.
In the end, Thompson marks it down to a generational thing-- some people are willing to share their voices and hear others, he says, and some just aren't. I'm not sure if that's true necessarily (I am pretty conservative on, say, my Myspace page, and pretty free with my Ventrilo joining), but either way, the use of voice chat in videogames has only just started to make itself known.