In his article
Grant Babcock says:
"The principle that the value of a currency can be traced back to a time when it was not yet a currency but just a commodity like any other is called the regression theorem, and interested parties can read more about it in Human Action Ch 17 § 4."
But he forgets to differentiate between intrinsic value and exchange value.
The intrinsic value might be zero (as is that of the USD), but the exchange value is much higher than zero, due to the specific properties of the bitcoin currency (anonimity, security, safety, traceability, non-inflatability etc...).
So yes, many times a currency starts as a commodity with non-zero value, but that's not an absolute requirement for a currency to be just that: a currency.
For instance, the intrinsic value of the USD started as a certain fixed amount of gold, then went to zero.
The property of it being backed by its artificial scarcity, caused by the requirement of all oil from the Middle East to be payed in USD, gives it a value as exchange currency.
Off topic:
That's also the reason why Saddam Hoessein and Khaddafi (and soon Hugo Chavez, and who knows, Iran) are/were/will be bombed into oblivion by the USA and its partners in crime, the NATO: they were going to accept payment in other than USD currencies.
Back on topic:
So, where intrinsic value is not needed, exchange value is, for a currency to be accepted as a means of exchange.