A fair point. Why do retailers accept USD, but not Euros or Yen? This is likely because most of their customers want to pay in USD.
This is correct. It is also because the US dollar is a world reserve currency that is generally the most stable.
But if they were to accept Euros or Yen, they would convert to USD likely if they are based in the US for two reasons:
1) their books are tracked in USD
2) their bills will be paid (including tax bills) in USD
Also correct.
So until their books are tracked in bitcoin, or their bills can be paid in bitcoin, it makes sense to avoid any risk in volatility, and they won't have the business case for keeping the bitcoins on the books.
It is more because their bills are paid in US dollars then the fact that their books are in dollars. There are plenty of companies that hold large amounts of foreign currency in order to pay their bills in that currency and then account for the exchange rate in their books
This will be solved as bitcoin adoption grows, and we start allowing businesses to pay their bills in bitcoin.
Bitpay, however, is a victim of their own success making transactions 0% - tough to beat that exchange fee.
bitpay is helping companies start to accept bitcoin. As more companies start to do the same we will probably see more business to business transactions which will not need to involve companies like bitpay and coinbase
It will be exciting to see how the future evolves! Cheers to 2015!