First of all, what's the cheapest way to move large amounts of money across borders?
You and other miners are the only ones who currently consider BTC money.
Secondly, who says they have to pay their supplier with the same currency they took from their customers? They can exchange it, and if the advantage in their local market is worth the hassle, they eventually will.
People like Walgreen's and Macy's are not trusting the livelihood of their businesses' cash flow with a stock that fluctuates 20% every day.