[mschuster91]

Or they want to avoid the problems that can arise with multiple systems having to authenticate at the system - some of which might use non-exchangeable ways of encoding stuff like Umlauts.

Or they want to avoid the customer service calls "I am in Russia and use a Euro sign in my password, how do I login?!?!?!"/"Help, I have a Macbook from my brother, where is the vertical pipe (|) symbol?" so they restrict the keyspace to azAZ09 for reducing this type of error.

[mschuster91]

Self-reply, as the edit window is out of order: don't forget mobile devices (the support of software IMEs for anything outside the alphanumeric range is spotty to say the best), and as you're talking about financial institutions, also think about ATMs and PoS terminals where the only thing you have worldwide available is a 0-9 keyboard.