"USD" doesn't exist online, instead users are making payments online in paypal-USD, bankWire-USD, or visaDebit-USD. But what about the other side of the world,

"USD" doesn't exist online, instead users are making payments online in paypal-USD, bankWire-USD, or visaDebit-USD. But what about the other side of the world, where payments are made in Alipay-CNY or Tenpay-CNY? If there's a chinese user of Alipay, how can you do business if you only have Paypal? Paypal-USD is not fungible with Alipay-CNY, they are separate payment networks (if you don't believe me, try to find an exchanger). The situation is like the days before SMTP, when AOL and Compuserve had different e-mail networks and a user of one couldn't send an e-mail to a user of the other. But BTC is easily exchanged for either Alipay-CNY or for Paypal-USD, so it is more fungible than both.