Exactly, and not only that, if you think about it it's unfair and doesn't paint a real picture of students' knowledge even if you do see tests as being able to show this true knowledge. You could have a hundred extremely apt students who would all be the best minds in the country, some scoring 100%, some 99% etc., but those that'd score, say, "only" 95% would get a D just because there're people that did a bit better. You could also get the opposite result where all students were subpar, but you'd give out A's regardless, since some would be less subpar. Therefore I'm completely opposed to curve grading, as well, because it leads to grades contingent on relative and not absolute knowledge.