The usual concern is the database storing the passwords/hashes being stolen. This has happened to dozens of small to medium size web services. The attacker could then hash away at the passwords to his heart's content. Then end-goal of this is to get user/pass combos to be tried on other, higher-value sites, like email services and, uh, banks.

Which gets us to the strange part. Who hacks a bank's service to steal a password DB in hopes of using the passwords against some other target? I'm thinking nobody. If you managed to compromise a bank's web service to that extent, you'd be trying to transfer all of the money from all of the user's accounts to one you control, not trying to crack their passwords.

That means that your bank's password storage method and complexity is not very important. What is important is that, whatever password you use, you never use that password on any other site. And that you use a bank that requires real 2-factor authentication, via text or mobile app or something like that, not with "security questions".