Surprisingly wide swings in fiat currency value can happen over the course of a month or two though. I imagine the volatility of BTC might cause problems for things like pre-orders.
I once placed a large order with a US company; unfortunately the order couldn't be filled for about two months.
I really wish they had billed me up front, because by the time they did bill me, the order cost 30% more in NZD.
While that's not quite the situation in question (you took my money and now I want a refund is stickier than "I want to pay you now rather than later" - in your case, you could always just cancel your order...), it's still relevant in that things could well have been reversed and (the bit I overlooked in my second comment) a rapid inflation in one currency looks a lot like a rapid deflation in others if you hold the inflating currency.
I once placed a large order with a US company; unfortunately the order couldn't be filled for about two months.
I really wish they had billed me up front, because by the time they did bill me, the order cost 30% more in NZD.