This really is organization dependent. Do your managers look over your shoulder and micromanage you? Would they get upset if they see HN in your web browser more than once or twice a day? Do you worry about them 'catching' you? Are you surrounded by 4 dozen people with multiple loud passionate discussions guaranteed to happen per day? Possibly in a language you don't understand most of the time? And whenever they do this making it very difficult to concentrate? Do they ignore your social requests to move it to a conference room, since they only last a few minutes and they're hunched over someones desk looking at something?
Do you know some people get a minor feeling of background anxiety when their back is to an open space with people talking and walking around? Their peripheral vision and senses conflict with the deep concentration required for software work.
Those noise cancelling headphones are meant to take out droning noises, such as AC system fans or jet engines in airplanes. Conversations with their lack of repetitiveness and human vocal ranges are not filtered out well, if at all. The music they will have to listen to filter you out is distracting in its own right.
Open Offices also decrease the barriers for interruption. Managers like it because they make their jobs a lot easier, because they get to hear what is happening and get status on their workers progress passively.
This is what open office means to many people.