In the beginning, BTC could be used to exchange of low value of virtual items, such as buying web sites or game points, virtual items, etc., afterwards, some people in order to get these virtual items, items may be in online auction own reality for BTC, others want to buy the real goods, but no BTC at hand, and then use real money to exchange BTC, as a result, BTC begin to flow, and have a "value".
In other words, bitcoin is inherently valuable as a means of payment; If it loses its function as a means of payment, it becomes worthless.
The value of money: it exists because of payment.
I think if bitcoin is not used to pay then people will not want to use it anymore. Because people use btc for the purpose of the transaction does not take a quick pay without getting back to work. So bitcoin should be considered a currency rather than a valuable commodity like gold and silver because its nature from the beginning is different from them