Re: Just a little question...
'It seems ludicrous that payment codes are still but four digits long.'
What security would it bring to make it longer? It's not meant to make bruteforcing it /impossible/, as would a login password, merely to make it easily /detectable/.
It only takes 3 incorrect tries to kill a chip, or have an ATM swallow a magstripe card, or any kind of connected POS to report that something's up to the central servers, and from then on, you're the proud owner of a useless bit of plastic.
For what it's worth, China Union Pay cards do use 6-digit PINs.