They aren't giving up enough information for anyone to use the credit card (which is your card provider's and Amazon's concern). They are only giving up information which Apple foolishly accepts as top-secret. The final four digits are printed on pretty much every receipt I get, and even using a shredder won't often separate them. TBH, Apple's reliance on the credit card number at all (let alone the last four digits) is pretty silly.
Yes, it's a flaw that you can get into someone's account. I was just saying that the credit card information being that available is not a big problem in my mind. Amazon clearly think the credit card should be kept more secure than the account, otherwise the whole number could be shown rather than just the last four digits, and I agree.
