How you going to pay in BTC if the person refuses to accept BTC..? Hold a gun to their head? You cannot assume away the point that I was making by saying, "if you pay in BTC" when you have not even gotten to that point yet, can you?
Of course. However some places do take BTC, yet I've never seen one whose prices are BTC nominated, and don't move with the BTC/USD price. So in reality the prices are still un USD (other fiat).
As long as they use fiat to pay for their supplies, their BTC prices will always move with BTC/fiat. To have truly BTC-dominated prices, everyone in the supply chain has to be BTC-dominated, and, sadly, that's still a long way away...
For now, fiat is a necessary evil, if you want to enjoy your riches. Sadly...