UNC seems a little bit different from other schools in ways like this. it seems as if they put more emphasis on the interview/school visit than other schools do. also, they don't have "grades" in their MBA program either. most of the class gets a "pass" and the top 10% or so of each class gets a "pass high", and the rare students that perform poorly gets a "pass low".
what other schools are you applying to?
I dont think they put any more emphasis on this than anyone else, they just come clean about it. Any school - I don't care which - is going to look favorably on a campus visit.
It does a couple of things
1) It shows you are truly interested (expense,time)
2) It lends credence to any claims you make about your knowledge of why the school is right for you.
3) It gives an unreal amount of stuff to use in your essays.