The assumption of 'unlimited natural resources' is now at odds with modern economic theory.
By seeing natural resources as limitless and by extension free at source undervalues their net economic contribution.
Take the example of massive ocean trawlers that cast kilometer wide nets then bring back all the catch to sell at market. The trawler is not creating the value of the fish just facilitating an arbitrage for the cost of delivery.
Companies are now looking at ways they can put a financial value on the value of their natural resource inputs.
A failure in quantifying and pricing resources creates a mindset problem when resources turn out not to be limitless or indescuctuble.
The World Bank, in it's 2011 report 'The Changing Wealth of Nations', set the estimates for all the planets natural resources - its forests, rivers, wetlands, wild lands, farm and grazing lands, minerals, oil and coal, oceans, biodiversity of speciecs - at about $44 trillion dollars, with $29 trillion belonging to developing nations.
Ref: HBR Oct 2011, the sustainable economy