I think people who have this as a mantra, lived in a time where most workers had the luxury of a real office with more sound proof walls. Even people with real offices tend to have paper thin walls when it comes to sound.

When I start a job every 2 years, I then to have my headphones off. Unfortunately the vast majority of background chatter tends to revolve around people's personal lives or just plain office gossip. Both of these things get regurgitated to me at lunch. I'd rather keep my focus. If they really want my attention, it's pretty easy to get through a variety of ways like IM.