Hi, Dig. Many of the states and local areas have regulations as to wearing high viz clothing. So, some of the "wearin' 'o the orange" is compliance with regulation, some is safety related, and some is fashion. As for safety, most North American shooting is dynamic, perhaps what you would refer to as rough shooting. Often it can have several groups in the same area and no inter-group coordination. Therefore, high viz can serve a safety function. Americans may well hunt with less training than in the UK, for sure less than in Germany.
American hunting attire evolved along different lines than did UK. Climatic conditions and vegitation are very different, to say nothing of hunting style. IMO, either line of attire will work either place most of the time. As for fashion, well, most people are a whole lot more fashion conscious that they are likely to admit. Orange can't hurt and might help - hard to argue with that.