I dont really know why, but it doesn't bother me after 4yrs u can get a job at school + finish off your last year of uni... thats what they told me in the info day...
plus it doesn't hurt to stay another year, and even when u finish there is always a job waiting for you!
UNSW tries to squish too much into four years. Most end up staying a fifth year to finish majors anyway. I think USyd does a more thorough job personally.
Being a five-year trained teacher also means you start one pay scale higher than a four-year trained teacher on your first year out.