From my experience, many students I've met in interviews/assessment centres are from either USYD, UNSW, Macq or UTS anyway. However, a large portion (around half or more) are from UNSW and USYD so I can see where the whole "do employers choose prestigous universities" idea comes from, but correlation does NOT imply causation.
The candidates selected are based on their individual merits and a large number happen to be from UNSW or USYD. Anyone from UTS or Macq could easily be in the same position if his or her individual merits are strong enough (I commonly encounter some amazing people from those universities in assessment centres), its just that there aren't as many.
This could be attributed to the size (in terms of student volume) of UNSW/USYD compared to UTS/Macq or perhaps the culture of extracurricular participation (I have some anecdotal evidence from friends who have transferred and say the big two have much stronger student society cultures than others...but obviously this can be biased since they transferred into the big two from other universities) or even just the average calibre of candidates themseleves (it is common knowledge that the majority of 'stronger' candidates end up at UNSW or USYD in the first place). However, there is no reason that anyone from another university cannot achieve the same because the opportunities are there.
In a way it's somewhat analogous to the whole idea that it doesn't matter what school you go to in terms of HSC results. There is no reason why someone from a low ranked school can't get a 99.95 ATAR (and beat most of the Ruse kids in the process) if the opportunities are there to achieve it. However, the differences we observe in reality are often due to external factors such as the fact that a school like Ruse gets the cream of the crop in the first place compared to others, not the school brand alone. In other words, simply going to Ruse doesn't increase the probability that you will get a 99+ ATAR, you gotta work for it.
A similar way of thinking can be applied to potentially explain why UNSW and USYD often get larger numbers in recruitment. Simply being a student in either does not increase the chance that you will get employed. It comes down to your own efforts in doing well academically and being active in extracurriculars that will determine how employable you are. It just so happens that many who choose to put in this kind of effort are from UNSW and USYD.
Also, if you have any intention of getting into commerce related positions (other than accounting), generally the recruiters hardly care about what degree you do let alone what uni you went to. In the end it often comes down to your resume and interview technique anyway because they can easily train you up on any technical stuff you need to know.