Our software lecturer/unit coordinator said that there's a university-wide scaling policy where they limit the percentage of students who can get certain grades, e.g. only 3% can get HDs... and for advanced/normal units, they pool together the advanced and normal students and do some crazy stuff so the 3% includes both advanced and normal students.... so obviously, most of them will be advanced students. If the unit coordinators feel more should be able to get a certain grade, for e.g. if there happened to be a higher number of people whos performance deserved that grade, then they can put the case to whoevers administering it, say to push it up to 5% for that unit, but apparently its not very easy to do so.
However I remember someone asked about scaling in one of the Eco & Business faculty's welcome day things, and the person said that from this year on there will be no scaling at all in the Eco & Business faculty.... so maybe it depends on the individual subjects you're doing as to whether there's scaling