Cubicles obviously aren't soundproof of course, but they're normally made with cloth-covered walls that do a pretty good job of absorbing sound, so offices filled with cubicles tend to be fairly quiet, and conversations don't travel far.
I think it's a reference to acceptable behaviour in different cultures. Tokyo station in rush hour is surprisingly quiet even though it's a sea of bodies.
Maybe, but my open-plan office here in Tokyo is much, much noisier than the cubicle farms I used to work in back in the US (back when cubicle farms were the norm).
It's not culture, it's physics. With a room full of a maze of cloth panels (which are specifically designed to absorb sound), sound is absorbed and can't bounce around the room, leading to much lower overall ambient noise levels.
