I would not let most of the current exchanges handle my money. Not just because of these numbers, but also because their compliance standards are low to begin with. If you are lucky you find a public proof of reserves audit, often by performed by non-professionals and leaving any governance unaudited. Making things even less transparent, Bitfinex for example is apparently registered on tax haven the BVI, the best way to operate under a cloak of secrecy - no wonder perceived credit risk is high! And then people wonder why Bitcoin is taking so long to go mainstream.