Real "money" is simply the most liquid commodity. period. Transferability, fungibility, etc, are only properties. Something can be a medium of exchange, a store of value and a unit of account without being money. What best eliminates the need for a double coincidence of wants? The most liquid commodity, whatever that happens to be, be it fiat currency, gold or heroine.
The fact is that Bitcoin probably won't be the de-facto world reserve currency, but it won't have to be. It's more analogous to virtual bearer bonds, but the threat of BTC possibly becoming real money will cause seismic changes in the system. As bitcoin becomes more liquid, it becomes more like real money. They dollar system will have to become more like bitcoin in order to compete.