What's the point of closing the door if it doesn't cut sound?
Globalization means everyone probably has the same door standards now...
Right of course. Just like we all have the same standards for electricity and power points. Doors aren't even standard between companies here, hate to think how they would manage to make them standardised with other nations.
But in answer to your question, a shut door in a office place has connotations above and beyond the doors ability to block noise. As stated early one of the most common is, door shut = unavailable. I know when I see a worker in a managers office and the door gets shut something serious is going on. If the door isn't shut, it is business as usual/non sensitive. This is despite the fact it is well known that the closest cubicles can hear any discussion above normal speaking volume.
However there are the other proviso's as well, for instance due to the fear of sexual harassment claims a mangers door can never be closed if the occupants consist of only two people who just happen to be of the opposite gender.