In what way are credits less confusing for users? If anything I would label them as more confusing, as they're a level of abstraction on top of money. They can make good business sense, certainly, as you'd rather hold on to the customer's left-over credits. And consumers can be more likely to spend credits due to the mentioned abstraction layer.

That said, they're a firmly consumer-unfriendly model, for those very reasons. And even then, the "more likely to spend credits" factoid only comes into play once they've actually bought into the system - seeing that it's Yet Another Credit System can be a slight added barrier to entry.

Expanding on this, if every place I spend money online worked with its own "credit" system, I would have upwards of 20 idle balances of my own money earning interest for someone else. Not a very palatable future.