Exchanges shouldn't be used as traditional banks.
They are similar in the aspect that they both hold large sums of money. And Bter was also giving interest on funds held by the users.
Like a savings account? If they are doing this, unless that interest are being paid from the exchange fees, they don't have 100% reserves.
BTW, I'm just aksing myself how they do to recover the stolen BTC. If they don't get it back, they should go to the market and re-buy those BTC. But a good question here is if they'll do this.