[adminprof]

Simply, because using absolute points would lead to debate over every single decimal of a point. A student with 89.95% would be determined to fight to get 90.05% and then continue to fight to get 90.15% so it only makes the problem worse.

[matheusmoreira]

That's not my experience. There were no A-F grade boundaries in any of the schools I've ever attended. Students only ever cared about the one boundary that still remained: minimum passing grade. I saw exactly one student trying to get a teacher to round up a 99% grade to 100% just so he could say he had a perfect grade, nobody else cared about decimals unless they were in danger of failing a class.

Boundaries are the problem. Standardized testing for post-graduate positions in my country would give students bonus points based on their overall academic performance. Full bonus points for grades > 90%, half points for grades > 80%... Of course students wanted to optimize that number as much as possible and I don't really blame them.