They fluctuate from year to year - depending on supply and demand, as asserted by Azamakumar and cem.
Case in point:
Law over the past few years at UNSW:
2002: 99.50
2008: 99.30
2009: 99.40
2010: 99.55
2011: 99.65
So yeah, it can go up, and it can go down. Clearly, in 2008 (Class of 2007)...