Hmm... I went to UNC undergrad and am now in med school here.
I would say that there is no grade inflation whatsoever for the undergrad science classes. (I was a science major, and I took a lot of science classes... the vast majority of them had a bell curve distribution for grades) - there's no grade inflation in the math or introductory level physics as well...
now I really can't compare it to schools like Duke because I didn't go there... but I can tell you that you have to put in some effort if you want to walk away with an "A" in your science classes at UNC... hope I answered your question.