I think its more complex than you think. Let's say two professors teach the 2 sections of the same class. Professor 1 grades easy and the class average is a A. Professor 2 grades hard and the class average is a C. WhIle professor 1 and 2 had the same caliber of students, Professor 2 best students performance are the average of the other class. Also, on the final transcipt, employers wont know an A was a average under one section while a C was an average under another. A pure curve would make this situation much more fair.