It's not only user interface, it's also security. A password is something that you have to remember. If you need 20 (distinct?) passwords, there's no way you ca

It's not only user interface, it's also security. A password is something that you have to remember. If you need 20 (distinct?) passwords, there's no way you can remember all of them, thus you'll resort to other ways to "remember" them. In most situations, this is actually lowering the security of the system.