WRT "Though if someone has their door closed they probably don't want to be disturbed." there was some cultural variation but every place I worked at, as opposed to heard about, it was a huge gossip worthy social faux pas to close an office door unless there was a private managerial activity going on in the office at that moment (yelled at, review, interview, etc). You closed the door at night or when unoccupied because you had $200K of hardware prototypes and protocol analyzers and laptops literally laying around unsecured. And it was a major social faux pas to open a closed door unless you were a resident of that room. Even if you were best friends you don't just walk in, any more than you'd dig thru their filing cabinet or wallet without them present.

90s office work reminded me a lot of dorm room life and culture. Dorm culture probably hasn't changed in the past couple decades, and having dorm rooms with doors hardly eliminates all social activity; if anything it encourages it and military basic training style barracks are not considered a requirement of socialization.