I feel like it makes sense to have something of your VCE success in your signature, or some other place where people can see it.
If someone wanted a tutor, they would want to see their tutor's qualifications - their Study Scores or ATAR or degree or whatever;
if someone wanted help on the forum with a particular VCE-related question, they would want to see that the person helping them is able to do so, and having your study scores can help to demonstrate this.
Why are there so many high ATARs on AN?
I think lala is right - it's common for someone to share something only if they did well in it.
Also, perhaps it's because the people here are keen for schoolwork, to the point that they join a site that is based around schoolwork, and that their keenness has brought them great success.
I think the issue then, if potential members ARE being scared away by the apparent abundance of academic awesomeness here, is to make them realise that us members are all here to help others out; not to just gloat over past achievement.