All these merchants are using a spot rate of the BTC to dollars or other traditional, universally accepted currencies. They are not using the BTC to price their

All these merchants are using a spot rate of the BTC to dollars or other traditional, universally accepted currencies. They are not using the BTC to price their goods and services, but they use the BTC as an extra form of payment. At the end of the day, those BTC are exchanged into dollars, or even right away, making the the dollar the de-facto currency you used for purchasing the goods or services.