"We have a pretty stupid banking system if you can..."

Yes, we do.

It's a complicated system that developed slowly, piece by piece, influenced by legislation, commercial pressures, other (contradictory) commercial pressures, and customers' needs. The need for backwards compatibility makes it impossible to rip up the old system and start again, and no one person is in charge of designing it. Naturally it's messed up and has inconsistencies.

---Meta comment: At first I was writing this with the intention of saying, basically: "Duh! isn't that obvious?". Now I realize that that's really unkind and unfair.

You've encountered something that you hadn't known before, and you "noticed you were surprised". That's a good thing, and it's good that you expressed it so that other people can realize the same thing.