no lol it's because the vce doesnt push you to your limits. ultimately, for each subject (chem, p.e., biology, for example) once you know the course, there's only so much you can be tested on. once you get above 40, everybody knows the whole course, and it becomes not about concepts, but rather not making silly mistakes, or answering the question in a way the examiner will identify as correct while skim-reading. sigh.
because of that, almost anybody who works hard enough can do well, because there's a very finite amount to learn. once learned, you're fine. the learning process, however, is easier for some than others.
im not saying im a genius at all, but i did very minimal work and did relatively well, yet still think the vce system is very flawed. i agree with ninwa - good subject choice is essential (plus doing well in english lol) plus a lot of work to learn the content inside out (if you're not one of those people who hear it once and remember it)