Four person cubes are not quite the open office concept, or don't represent all instances of it. In Japan, open offices include everyone. You look away from your monitor and there is your boss ("buchou" -- department head) looking back at you! If you have to leave before the buchou, you apologize, e.g. "O saki ni, shitsurei shimasu".

If the boss is not there, then it's not quite the open office; it's a slightly strawman version of the open office which doesn't quite include everyone. Even so, the boss can come out peek at the workspace at any time and tell at a glance who is there and who isn't, and who is doing what.