from my understanding it's simply because there is a clinic or something that runs in the same building and they want the students to look presentable. Ties, etc. not required...
there really is no strict dress code, pretty much people wear whatever is comfortable...jeans,shorts,windpants, basically whatever. there is a dress code for preceptorships but that is all.
Let me echo Bostongirl22's reply - there is NO dress code at UNE for classes. People where whatever they want. I've come to school without shoes on in scrubs and a ratty rafting fleece, hair not combed but in a bun anyway... nobody cares, and certainly nobody says anything to you. So if there is some secret dress code that nobody has told me about in the last two years, it's not very well enforced!