And of course nobody is using Teamspeak or Vent when playing RnL or any other game for that matter.
Even if you cannot talk to your entire team generally nobody will use something like team speak, as its too much of a bother. Even if someone spams to his entire team to join his TS channel to get a communicational advantage hardly anyone will join.
Sure in clan matches or among friends people will use external voip systems. But that is because you need to be able to talk regardless of the server someone is in.
However good or bad the in-game voip is, and no matter what abilities it got, the in game voip will be the primary method of voip communication in public games. In the worst case scenario most people simply won't use any voice chat at all.
The main thing for me is that voip with a big group of players quickly gets cluttered and becomes useless for teamwork. For public play small groups of 4-5 people playing together and communicating among each other make communication and teamwork a lot easier.
Now to aid teamwork for instance Squad leaders should be able to talk to the entire team, but for other regular soldiers. I think it's actually better to limit them to local chat just to keep things simple easy and uncomplicated.
Even with Iron Crescendo on teamspeak the teams were divided up into separate groups to make communication useful and not cluttered..