I bought last years Artexpress CD catolouge and on there it had an interview with the AGNSW curator and the Homebush curator,
the AGNSW one said he was going for things that would grab audiences attention by either - being created from something that art is not usually made from... dealt with an edgy concept/subject matter... and his favourite was works that involved the audience in some way - hence that awesome train security one where the viewer was shown on a security screen looking at the work/using the magnifying glass to look at the work etc..
the Homebush guy on the other hand talked of "the Journey" as a theme, which I thought was completly crap seeing as though we do that in English, lol, but whatever.. alot of the works from there just seemed to be generally good and were thus selected..
Personally, I think anyone should be completly stoked if they get nominated, let alone selected (and Im not so sure about the political thing, because last year my school [St Ives High] had 3 students in the AGNSW exhibition)