No, as I said before, it's about learning what courtesy is in the new context. In some schools this follows from an attempt to keep some semblance of the rules of courtesy found originally in the art (mind you, that's usually an attempt to maintain what would now be outdated norms even in the country of origin). People coming in don't know that context, so they have to learn something new. This practice is something that helps develop the skill of discipline. It also helps people be more mindful of their context (we behave differently in the training hall than we would in the street) which can be another useful skill.
I never said anything about anyone being reprimanded. In the dojo's I trained in, there would either be a reminder (often from a senior student, sometimes from the instructor) or simply a bit of silence to give the student a moment to realize they'd left off the "sir" or "sensei" that is the norm. It's a bit uncomfortable for a new student (as is any new situation and new set of norms), but people tend to adapt to it within 2 or 3 classes.
And I understand the cultural difference that exists. I think the "sir" may be easier for folks to adopt here in the Southern US than in the Northeastern US, because many here were raised saying it, anyway. It simply doesn't have the connotation it carries in the UK. There, trying to use that same approach would possibly be counter-productive, because of the cultural context.
