Yeah I think by proxy the people who find ATARNotes are the people that are really keen on school. I was researching Psychology stuff and stumbled upon this site. I'm sure many others were googling VCE things that would give them an edge and found it. Obviously, the people who want an 'edge' are the people who are aiming really highly. So I guess the scores correlate with the aims?
Could also be the prevalence of students who go to top schools (or maybe I'm imaging things?? I have no data to back me up) but I see a lot of people from MHS, and I've seen one person from Cranbourne Secondary, and no one else from any school around my area. That could be an off-shoot of my first point, though.