They do get stereotyped a bit and I think sometimes it is unfair. That being said, most of the selective kids I know are much more school/uni/work focused then most of my HS friends, or people I know who went to a comprehensive school. Like, a lot of these students are conditioned to think "get top ATAR - get into top Uni course - gun for top graduate job". It's not an obvious trait, it's just something subtle I've noticed amongst people I know who go to such schools. In contrast, with most of the guys I went to school with who did well (90+ ATARs), that mentality and focus isnt as influential on them. For example, one of my mates got a 99 ATAR and studies Law. Despite having a good shot at top graduate positions, he isnt really keen on gunning for them because he doesnt want to be stuck working in a high pressure role with long hours. With a lot of my selective friends, they dont really question that aspect of work, they just seem to gun for the top positions because it's a part of their conditioning if that makes sense. A lot of people will probably disagree and I am generalising, but it's something I've definitely noticed from hanging out with different people.
In terms of BoS, the demographic obviously features a lot more selective students and I think that has led to the development of some unrealistic views on education. There seems to be a mentality whereby people think the HSC is easy and that anyone can do well. I think that has largely been spread by selective students who are surrounded by highly capable individuals. Having gone to a comprehensive school, to me this view doesnt really sync, because I saw people who struggled a lot with school (I knew a few people who could barely read by the time we got to Year 12).
This post isnt a selective bashing, it's more or less my observations on the differences in mentality between selective students and others. I am generalising, but I do think there are subtle differences in mentality with such students.
Also to note, when I say "selective", I'm referring to any school which selects students on an academic basis (so private schools like Knox and Sydney Grammar are included).