from "Practical .NET for Financial Markets":
To protect the integrity of the market, precautions must be taken to ensure that no credit defaults take place. As mentioned in Chapter 1, this is the job of a clearing corporation, which takes away the credit risk concerns of large players through novation.
Right. We're in trouble with Mt. Gox because Mt. Gox is not just an exchange. It's also a depository institution, a broker, a clearing house, and a transfer agent. In the real world, those functions are separated to prevent Mt. Gox type situations.
NYSE Euronext, for example, is an exchange. They take in orders, match them, and issue transfer orders to a clearing house. At no time does the exchange have ownership or possession of the items being traded. The transfer orders go, usually, to the Depository Trust & Clearing Corporation, which does the actual transfer of stocks, etc. from one owner to another. They're like the Department of Motor Vehicles for stocks.
Customers deal with brokers. Brokers have possession, but not ownership, of securities on deposit with them. Brokers may hold customer cash, but large customers usually move their cash out daily to a separate bank. (It used to be common to sweep cash into Treasury bills overnight, but interest rates are so low now it's not worth the trouble.) Brokers in the US pay into an insurance fund, the Securities Investors Protection Corporation, which insures each customer for up to $500,000. (SIPC paid off the first $500K of customer losses when Madoff was busted.)
These parts of the system are the plumbing of the financial world, and work fairly well. (Most losses, fraud, and other trouble comes from investment funds of one kind of another, because funds actually own assets and have customers as creditors. Funds also get to make investment decisions about their own funds.)
In the Bitcoin world, too many functions are concentrated into "exchanges". In particular, exchanges today are depository institutions - they hold customer funds for extended periods, not just during a trade. We need exchanges that work more like Coinbase - every day, if you set it up that way, all your cash at Coinbase is swept into your bank account.