Well whenever you take a break from coding you would know that everyone around you knows you are not working. This can be needlessly stressful and would probably lead to people overworking themselves and burning out.
no no, it's not an issue of people actually caring how much you work. I agree that people aren't going to call you out or tell you to work more. It's more of a self-consciousness about taking breaks. People are much harder on themselves than they should be. We try to project an image that we are hardworking and that we don't waste any time at work.
If people were always looking over my shoulder I wouldn't be comfortable having HN open in a window/screen for half the day