Bitcoin even offers a bit of extra support for that too, via transparency, based on the public blockchain. There is embedded protection against third parties: if a rogue employee of the bitcoin-bank transfers bitcoins out of your bank-wallet, the transaction can be followed. It might not be possible to recover the money, but at least some kind of identification can be performed - with the help of the bank and with legislative support, this can be enforced. This transparency is not there for tradicional banks: if there is a problem, you trust them to solve it, but you can not independently see what happened to your money.
This relies on the fact that anonymity is a fragile concept in the bitcoin world: an address is anonymous as long as nobody puts the effort (and has the right extra pieces of information) to correlate address to person.
At the end of the day, it will be a matter of the bank having a business interest in keeping a clean reputation. This is too early for the bitcoin economy, so I would not trust any online bitcoin bank with more than a couple of bitcoins. CitiBitcoinBank is not here yet.
It's worth noting what happens in the real world: Most folks do not store their own. They instead rely on banks and trusts to do the job. Those are backed by various types of insurance.
I suspect that sort of ecosystem will need to evolve for bitcoin too, since average joes don't know to protect their digital wallets.