Whilst I'm only speculating, I would possibly argue that a bias in the criteria towards native species is the point - Australian species have the greatest potential for breeding programs in Australia to have a direct conservation impact.
That's not to say that I don't believe non-Australian species should be housed and bred in captivity in Australia - I see the value in people being able to view and connect with animals from across the world in easy access from where they live - but that, with the resources Zoos Victoria have available to them, I suspect they would rather dedicate these resources to species which can have the maximum impact in terms of conservation, education, etc.
I do think it's a valid question about common, small species like meerkats, otters etc, and where they fit. Meerkats, arguably, have a place due to Melbourne Zoo's connection with the children's hospital. The idea that enabling is a super-category makes sense, although kind of undermines the concept of having categories in the first place
Are the siamang on the Japanese island the older offspring of the breeding pair, with the others in the orangutan complex, or did I imagine that?