I don't think they were disgruntled with the grades that they actually got. From what btilly said, it seems that the frustration occurred before they received their final grades because they didn't realize that the grading system was going to be fair. They expected to be graded relative to each other (on a curve), with A's going to a certain, pre-fixed percent of the class. Instead, everyone who did well got an A for their good work. I think the complaint was about the demoralizing effects of the erroneous assumptions during the semester, not about the grades themselves.
Grading on a curve is a strange idea. It completely destroys incentives for pear to pear learning, that was very important part of my college experience. I learned a lot by explaining material to my peers. It would be much harder if there was something as discouraging as grading on a curve.
