Or they could operate using fractional reserve method, a 90% reserve is still much much better than any banks which only have 10% of client money at hand.
That's not what "fractional reserve" means. For a bank, a loan is an asset - someone owes them money. Banks get into trouble when many loans go bad, as happened when the real estate bubble popped. Or they get into trouble if they have short-term deposits and long term loans, and too many depositors want their money out at once. That's not Bitstamp's situation. They don't own 30-year mortgages. They have no big illiquid assets they can sell off. They have nothing except their customer balances, and, according to their financial statement filed with Companies House, a few hundred thousand in paid-in capital.
Bitstamp needs $5 million within days, or they're going into bankruptcy.
