Yes, transacting in fiat currencies will mean counter-party risk. But Ripple does many things to mitigate this risk. For example, issuers cannot freeze or modify balances. An issuer that refuses to redeem balances for one party can't stop them from exchanging their balance for a balance at another issuer. If an issuer refuses to redeem balances or delays them, the instantaneous value of their balances will show in the exchange, driving their customers away. And, of course, each user gets to choose their own issuers with numerous features to keep payments seamless and avoid default chains. (Payment chains exist only for the instant a payment is made.)
This confuses me if the guy issuing DYMs refuses to send me my dimes on demand, how do I exchange those DYMs to another issuer. Someone has to lose out on that transaction no?
And when you say "if an issuer refuses to redeem balances or delays them, the instantaneous value of their balances will show in the exchange." I'm not sure what this means. Can you give me an example? I know you are saying it will be clear to everyone that someone is defaulting, I'm just not sure how that happens or what you mean by "their balances." (or where that can be found).