As BTC is becoming more and more used, the markets take to a compulsion of accepting BTC as a form of currency in exchange of the good and services. It is indeed interesting to note how Bitcoin in spite of all criticism is only proving to be that of a great success.
Like gold, Bitcoin's supply is limited and durable, digital gold and like fiat, its divisible and portable, currency, it's the potential future of Bitcoin, but now realistically what gives it value is its price, more of speculation, people investing expecting its price to go up, so IMO it's entirely true that currently Bitcoin derives its value from the possibility to trade it for fiat, not a realistic value.
The real valuation/usefulness of Bitcoin is in its properties as money, store of value, medium of exchange, and unit of account.