It would be fabulous to have the ability to edit a CC. I have a Bank Card/CC that the number never changes but the expiration does so it sucks to have to remove my CC and add a new one so the ability to have edit it would have been fabulous!

i think its done for security more than anything else to stop people who hack your account from stealing your details. You'll find this is a common thing across the entire e-commerce world.

Updating a CC isn't any more of a security risk than adding a CC, as long as the original CC info isn't displayed fully.

Storing a CC in the first place is a security risk. PayPal rocks =p