I think it is up the each faculty as to exactly what policy they have for bell curving/what percentages they can give out
For example, in Law at USYD:
"4.1 No more than 40% of the students may receive a grade of D or above.
4.2 The range of HD grades must be between 3-10% of the total number of students.
4.3 A minimum of 10% D grades must be awarded."
This applies for subjects that have more than 25 students.
The reason law introduced this a couple of years ago was:
"The purpose of this policy is to ensure an appropriate degree of fairness and consistency in assessment. It will allow a meaningful comparison of marks, where a grade given in one subject signifies a level of achievement that is similar to that reflected by the same grade in another subject. In this way, the standardisation policy aims to support students (by promoting fairness and transparency), to assist academics (by providing appropriate guidance in their assessment of students’ works), and be more useful and transparent for other universities (who look at students’ grades for accreditation and admission purposes) and for prospective employers. The standardisation policy also aims not only to ensure an appropriate degree of fairness and consistency in marking across a particular year, but from year-to-year, to ensure relative stability in the level of marks awarded, and to maintain the integrity of the marks given and to avert “grade inflation” and its consequent impact on the award of honours and ranking on graduation."
Basically they thought too many students were getting D's and it was de-valuing the degree. The idea is that technically one year of law is not going to be dramatically better or worse than another year, and this way standards are maintained despite different markers/teachers/course structures etc.
