Actually I suspect there may be a connection between the currency the economy uses to divvy up scarce resources and whether wealth is zero sum. If wealth were tied explicitly to the amount of gold humanity had extracted from the earth then the sum total of both are assumed equal. In that case, wealth definitely appears to be zero sum. It could even become negative sum if some quantity of gold is being made useless or unavailable. If currency is not tied directly to some hard-finite asset like how ever much gold has been pulled out of the ground then maybe wealth can be positive sum.