They might not have had any resources, but was this really a problem considering there was no outside threat? A civilisation like the Aboriginals would've been quickly conquered in Afro-Eurasia, but Australia was largely isolated. Australia has been entirely Aboriginal from the time it was first settled by humans until European colonisation. Resources or no, in their 40,000 year history, were there never any great conquerors who tried to form coalitions of tribes/states? Nobody ever declared himself a King and began to subjugate weaker tribes? It just seems so unlike most of human history.
The real question you have to ask is why this WOULD happen? A great leader rising up to dominate others only makes sense if there is something to gain. However, one of the characteristics of hunter-gatherer societies is that they don't produce substantial surplus (see any description of early human living, but special mention to Chris Harman's more accessible work A People's History of the World). That is, there'd be nothing to pass up the chain to this hypothetical conqueror as spoils.
Larger, more complex societies are dependent on a social layer freed from the labour of food production so that they can devote time to organisational tasks. Typically, this means agriculture. While agriculture certainly developed independently in several locations around the world, it never did so easily or without reluctance. Basically, farming is hard. India's history provides a rather nice example: when tribal living was being changed gradually into sedentary agricultural life, many people instead fled into the forests to maintain simpler lives (Paul Siegel, The Meek and the Militant).
There has also been some speculation that pure chance played an important role. Although Diamond's work Guns, Germs and Steel has many, MANY issues, it does make an often-agreed-upon argument that Australia's uncooperative fauna played some part. Essentially, there are no suitable beasts of burden for large-scale application making more complex societies relying on extensive trade or intensive farming impossible.
It's also worth mentioning that while these arguments apply to many parts of Australia, Indigenous Australians had quite diverse ways of living. Some included rather large, permanent settlements which engaged in agricultural activities such as yam farming and eel farming (see the work of Heather Builth for more on this). In other regions larger confederations of tribes could form, although size and practical interactions were limited by the constraints of nomadic life. However, it is true that even these larger settlements and tribal confederations still never approached anything resembling cities or states.