Low cost and easy implementation are sound arguments. But exchange between currencies is really not a problem with credit cards either. It is no problem to do online purchase in a different currency than your own with a credit card. The card company do the exchange for you. (and their exchange rates are not bad)
I was just giving some end use examples. These type of things could be done with or without your bank. Once something is in Ripple you can work with anyone else in Ripple. So if someone gets in through their bank and I get in through my bank, we can do transactions with each other that don't involve either of our banks. I could pay you BTC and never have touched a Bitcoin, if that's all you take when we do a transaction (and no banks need to be involved). This is why I am saying that I think reaching a critical mass of users is important in Opencoin's business plan (my opinion only - I don't have anything to do with Opencoin Inc.) before they release the open source code. Users are what will make Ripple powerful as a payment system - not the price of xrp (or even xrp at all).