I think whether people use voip depends on the game and how well the game facilitates it. On TF2, sometimes half the team is using voip, but then again, alot of these guys are in the clan that own the server. Also, certain TF2 servers are like communities because of regulars, so people get comfortable and use voip, which is a more personal experience than typing. Quake war servers were few, so there was a sense of community as people recognized each other, I remember I used voip alot, sometimes others would too.
BC2, I have put a about 20 hours into multiplayer and remember hearing maybe 1 or 2 guys. They make it a bit complicated as you can voip with your fireteam or with your team and even with the other team, so you have to think who you want to talk to and which button to press.
The difference with TF2 and BC2 is also the setting and style, whereas TF2 plays and looks more casual. I guess, my point is that TF2 has a friendly, non serious vibe which facilitates voip because people are much more comfortable interacting with others. Also, I dont play BC2 enough to have an informed opinion on it, but like, how often in BC2 chat do you see someone not complaining about their team?
And since we posting funny videos, here’s one related to TF2 and voip 