From my experience that seems pretty normal. Our means were usually in the C/C+ range, and <5% A also seems pretty normal. I'd estimate it has more to do with the ratio of good students to bad students than how hard the class actually is, if it's anything like my school.
Edit: I think that I feel this way because most of my classes were not curved, and almost all of them had very similar distributions. Classes that most students tend to find very hard (physics, organic, biochem, pchem) have very similar distributions to classes that most people find relatively easy (biology, gchem). It seems like C students just put in however much effort allows them to pass the class, B students put in more, and A students do whatever it takes to get an A in whatever class they're taking.
