If they have the money to put into a successful product there is no reason they would limit themselves to bitcoin commerce solely unless they were selling a product market towards bitcoin such as asics.
The main obstacle here is that fiat money has already occupied the position of transaction medium, people have little motivation to use another transaction medium if the seller does not accept bitcoin exclusively
You are buying something from an europe online merchant, they only accept Euro, you pay with your credit card, and the credit card company do the conversion: Buy euro at foreign currency exchange and pay the seller. So if more US people are buying europe products, then Euro's exchange rate will rise
It's the same for bitcoin economy, if more people are buying goods/services that only payable in bitcoin, then bitcoin's value will rise. On the contrary, if more people use bitcoins to buy products payable with fiat money, bitcoin's value will drop. For example the recent price drop is related to that kncminer was converting lots of coins to fiat money to pay their chip manufacturer who only accept US dollar