This is a major misconception, because
merchants don't have to hold Bitcoins to accept them.Why? Because services exists this times that handle the payment/exchange process from Bitcoin to the fiat currency of the merchant's preference and availability inside the service itself right away. Extremely easy.
Example:
https://bitpay.com/retailIs this what I think it is?
You can accept payment and then quickly convert it into fiat right away with the current market price?