The ironic thing about this is that the nature of Bitcoin (specifically, the fact that all transactions are recorded in the blockchain) means that auditing a Bitcoin exchange is an eminently solvable problem. To my mind, given the ease with which Bitcoin wallets can be created, any exchange that commingles its clients' Bitcoins should be viewed with suspicion.

Yes, it's easier to dump everything into a few wallets, instead of maintaining individual wallets for every client. However, if the team behind an exchange isn't capable of dealing with the complexity of individual, segregated wallets, you have to wonder whether they're competent enough to run an exchange in the first place.