Although people may not have necessarily studied, they may just be good at learning things over the year, and just absorbing knowledge.. so in a way they did study.. subconsciously?i see where you're coming from, but it's just ridiculous that i spent 1 week studding, while some people where not bothered and smashed my marks big time.
But seriously don't worry, a fair bit of SC is like skills and stuff, and there's some stuff you just can't study for.. you'll be fine for the HSC.