It is completely arbitrary in the US too. Most parents will berate their children for getting a B- or C in grade school, even if that translates into 77 - 82% of some complicated problems done correctly. There were some courses I had in college where showing up and doing the homework guaranteed a 90% and the last 10% was just test grades. They might have been low 100 level courses, but someone gaming the college system can get a 4.0 GPA taking all low level courses except the bare minimums to get their choice degree, have less knowledge than someone with a 3.5, but get hired easier because the GPA is high.

Often the grades will follow a gaussian (normal) distribution. In that case, the wider, less used range, is important in capturing and quantifying the outliers. It would be an effective grading system if it saturated at the high or low end because it would no longer have the power to differentiate at the saturated end.