Right now, Steem has value because you can exchange it for bitcoin. I don't have to exchange bitcoin for fiat for it to have value for me, even though the merchants accepting it are likely exchanging it for fiat. I can and do spend bitcoin all the time. I've never exchanged it for fiat but have always exchanged dollars for bitcoin. I prefer to have my weath stored in bitcoin. Someday, the merchants will, too, and few will care what the exchange rate for bitcoin vs fiat is.