According to this link, for the 50th percentile, Aboriginal Studies is the lowest scaling subject with a scaled mark of 12.6/50. In contrast, Drama has a scaled mark of 23.9/50 and Mathematics Extension 2 has a scaled mark of 44.3/50. Depends on your definition of scaling, tbh.The statistics for scaling in 2012 have not come out yet because the HSC for 2012 has not been sat. However the scaling stats of 2011 are available.
From this you can see that is definitely not the lowest scaling subject.