Getting credit card info might not be for pay purposes at all. Maybe even now PSN is not looking for people to pay for its service... like XBL.
Then why the credit card info?
Ok. I'm theorizing off the top of my head so please bear with me. Ask an illegal immigrant how hard it is to get hold of a credit card, prepaid or otherwise. You have to provide a valid SSN and the name that goes with it. Add to that the need for an address for billing reasons. So now you see that only valid, legal residents of the US will be the only ones are going to be using PSN in the near future. They cannot ask for your SSN for a gaming service but using a credit card to be able to sign up for your game account they're effectively placing an ID on you.
For the next step only the name of the real card holder can be used to sign up for the account. So let's say that you get banned for some reason (CFW?). Now how are you going to sign up for another account? By using a different CC? Well you "different" CC still has your real name attached to it. How about instead of banning your user account they ban YOU! You cannot sign up for a different account from PSN! You cant use a fake name because the CC will be declined. So you have to use your real name (and it extends to your SSN) and they dont/wont let you back on with their service.
Welcome to PlayStation America!
They've clearly stated that they can change the TOS as they see fit. Why cant they have progressively draconian measures? Maybe sometime down the line they'll start charging for their service... but at the moment they can use this method to weed out the hackers, modders, homebrewers and other problem children!