No one going for IB from usyd/unsw expects their university to be a distinguishing factor because a good bulk of other applicants who make the cut in sydney offices will also be from those universities. I really wouldn't want the person flicking through CVs to have no idea about the differences between universities (specifically marking etc)
Sometimes, going to uws may not allow your box to be 'checked'. IB is a long shot, I am interning at a big 4 at the moment and out of a cohort of over 70 ish interns (55 in audit, the rest in others), there is 1 guy from uws and that was his 'special fact about me'. So no, it is not 'all the same' - the students, opportunities available to you etc, vary significantly between uws and 'top' universities.
OP, if you have your mind set on studying a combined degree, specifically with law, just do it at uws because its very easy to transfer after 1 year if you feel the need to.