I suggest you try to take the perspective of the top school.
Lets say you are a James Ruse student. Hardworking and smart ( usually ).
Your level of learning is much greater than most other students.
Would you be happy and content to be learning a year 9/10 syllabus while you have the capacity to learn more ?
Although they may not follow the Board of Studies syllabus, it's because they already have the knowledge of pretty much everything that is to be taught for that year.
Conversely, a school with extremely poor acedemic students also tend to have teachers that don't teach the syllabus. Rather, class involves a whole period of useless bludging and mucking around. Would you say it is unfair and that they are cheaters because the teachers don't teach the syllabus? The difference is James Ruse is teaching year 11/12 material, while the poorly acedemic isn't teaching the syllabus at all. Both of which are not following the official Board of Studies syllabus. I wouldn't call that 'cheating'.
As said before, James Ruse does not have 'special' scaling that makes them top evey year. Please refer to the technical arcana fora for more information about how the moderation process works.
Lastly, you can't expect that every school in NSW should be expected to strictly follow the board of studies rules in terms of teaching. If say James Ruse was forced to learn at the same rate as other schools, there wouldn't be any schools that specifically stand out. In my opinion, it's a good thing that it is known that these schools are the most acedemic and represent the elites of the state.