As a merchant, it could hypothetically be easier or cheaper to deal with Bitcoin than other currencies online. (For example, note how aggravating/risky PayPal is.)
It's not. Given the volatility of bitcoin you're taking on a lot of currency risk since the value of the bitcoins you just got for your widget can change a lot in a few days. The extra cost of conversion and/or hedging is not worth it.
Especially when you consider all the other problems that bitcoin has.