Bitcoin is a community currency that requires self-policing on the part of its users. In contrast, established fiat currencies, where cash, coins, or their digital versions, have value by dint of regulation or law, are underwritten by the state.
Bitcoin may be useful for trading goods and services but it does not yet allow borrowing or lending. In the physical world this happens through financial intermediaries: you put money in a bank, and someone else borrows it. And though a virtual Bitcoin bank might spring up, that would raise questions of its own. How would a saver be assured that he would get his money back when he wants? If a bank got into trouble, who would be the lender of last resort? Typically, the answer is a central bank.
In other words, Bitcoin is technically sophisticated. But for the time-being, it's a fairly primitive monetary system.