If I put a valuable antique coin in a bank's safety deposit box and the bank closes due to bankruptcy, I could sue to get my specific coin back because (a) the value is in a tangible item that, (b) the expectation is that bank is storing an item that is still specifically owned by me.

If the bank was merely holding my money in an account balance, then I could not sue in this manner since I would be treated like any other debtor in the bankruptcy proceeding.

Someone tried to sue MTGox to get their money back as if they were in the first situation. The court correctly ruled that the plaintiff was actually in the latter situation and they would have to be treated like a debtor.