Well you see to maintain a decent quality of life there needs to be a steady rate of investment into housing,... so I can't see how it is an unproductive asset,.. If you took away the private developers and Investors I would hate to see the state of the housing market.
Very few "property investors" are developers. You shouldn't even use both terms in the same sentence. The vast majority of the "property investors" that have emerged in Australia are little more than property flippers. They buy existing properties (on credit) with the hope of selling for a profit later.
Developers who actually use their own money will still be profitable in the event of a severe correction, because construction costs are still low. Responsible developers in the USA are still making money, despite a 20% price slump. Only the highly leveraged developers are at risk.