It's economics 101. If you can build a product for less than what buyers are willing to pay for it, then you might just have a business.
Money on this planet is all about emotions - its all about what people are willing to buy based on its perceived value. The only reason that housing prices are going up in Melbourne is because people believe that the houses are worth more right now.
However, as in the US market, people will all of a sudden believe that the houses are worth less (for no real reason) and the market will tumble.
Demand + perceived value = actual value. There's nothing else to it