Should grading take all students' performance into account? This question is partially related to this question.

By trying to understand which one is the correct way to grade an exam I came out with this doubt. Should each exam be considered as independent or should a mark be assigned based on the other students' performance.

As an example


if all the students final exams are from 80% to 100% correct should be considered the fact that the exam was too easy while grading it?
if all the students final exams are from 30% to 60% correct should be considered the fact that maybe the exam was too hard while grading it?


To resume, while preparing/grading the exams should the results respect somehow the normal distribution or should each one be graded independently?

EDIT:

Based on my career as a student for every exam we had statistical results from all the students (min, max, avg) with the grades distribution. Most of them respected the normal distribution. So what it is not clear to me is if it depends on how the teacher create the exam, on how it is graded or just on how usually students perform.
I'm going to give this from a student perspective, so take it with a grain of salt. But I can say that I would hope I was graded independently of any of my peers on a given assignment*. Simply put, I want to be evaluated on my progress relative to the course objectives. I'm not interested in my progress relative to everyone else's.



* That being said, once the independent grade is assigned, I don't care about or mind any post-grading corrections (a.k.a. "curves"). But again, that's after my exam is independently graded - so I can at least see the raw grade first.