Is it still uncommon ? I have been in games where some someone led by giving orders. Most of the team members, including myself, kept quiet but we followed the orders. That's sufficient for me.
Some people like to chat with their friends while fighting aliens, I find that distracting (but didn't really care enough to do anything).
So yeah, few people may talk but I don't think it's game breaking. Most of the time, people knew what they were doing and they looked out for each other.
It's people who don't know how to play well (e.g., Medics who don't heal comrades, SpecOps who don't dish out ammos, ...) that kills a game. Some have mic but simply ignored everyone else (or they only chatted with their friends). In general, people who need help will yell "Ammo !" or "Medic !". Not sure why they wouldn't really -- unless they think they are well taken care of (like me ! ^_^).