if you are using bitcoin then maybe today 1 apple is 0.0008 btc , but tomorrow with 0.0008 btc you can buy 2 apples, but if no one used bitcoin for shopping then there won't be any shop that will adopting bitcoin anymore
so what will be you choice?
The reason to pay through the Fiat only is not only single .
Think here throughly that what will happen if the price of the Bitcoin sudden increase after hour of the payment .
Here Fiat payment remain constant and take less charge as an fee but in case of Bitcoin payment we will face more problem ,.if the price increase after payment then our mind will say to own again and again that why I made that payment .
secondly the shopkeeper will not direct trust on you for the direct payment and go away , he will wait for atleast one confirmation because the reverse in the payment of the Bitcoin is a common thing before the confirmation .
So here we need to do something more changes and development then we can say that we will pay in Bitcoin definitely .