I don't know the details - but I believe that the scaling is done at the discretion of the lecturer-in-charge.
For example, in COMP1711 - Richard had told us that 1711 was scaled such that, generally, 1711 was 20% higher than 1011 - results in more HDs and Ds given out in the higher class.
But of course, their idea of scaling is not some "advantage" - rather its to compensate you for the harder work you've done, so that say if I got 90 in 1711, I should've got the same mark in 1011 if I put the same effort in.