I think this is a bit of a silly question. There is no definitive answer to this. There are no short cuts in maintaining a H1 average. For most people, you need to be on top of your work, be up to date, constantly revise. It isn't easy. If you are one of the exceptions which take less time to do all of the aforementioned, there is still the challenge of being able to be familiar with the expectations of all of the subjects that you do and being able to allocate/prioritise your time effectively. I know from experience, the way I study for most subjects has to be tweaked for other subjects because the expectation for that subject is higher and therefore I need to allocate more time to that subject. Sure, there might be one or two subjects during your degree where you will get a H1 easily (as a result of cramming, highly reliant on wrote learning). But you can't with most subjects. The expectation of University is a whole different ball game to VCE. The two can't be compared IMO. Some of my friends who got a 98 ENTER have had to extend their science degree by an extra year because they haven't been able to make up for their failed subjects. Some of my friends who got high 80's for their ENTER are now on their way to doing postgraduate medicine. There isn't any correlation.
My general answer would just be: It's very difficult for some and not as difficult for others because of what I've mentioned.