There is risk between banks settling through the CHIPS network and Fedwire. Since forex is not centralized in one exchange a bank from anywhere can exchange money with another, the contracts between the banks specify a delivery of the currency. This means you could possibly make a trade with a bank who does not have the capital to deliver the funds by the specified time, putting the money that you deliver at risk of being tied up or being completely lost. Efforts to remove this risk from the market have been put in place, such as real time exchange of the currency but this usually costs more to do which is why some banks still settle at the end of the day instead. The CME can closely regulate trades becuase most brokers who put in your trade have capital requirements to maintain and are very closely regulated. If a broker were to go belly up the CME would stop acccepting their orders unlike forex where a bank that is essentially bankrupt can still make trades with other banks all trading day until settlement time comes around.....then it gets ugly.