21st Century Digital Boy

Why does my Xbox 360 not allow me to remove my old credit card from the list of payment options? It expired almost half a year ago, and both my 360 and Xbox Live know this.
Furthermore, why does my 360 even allow me to select this credit card for buying stuff with on the Marketplace?
And, most importantly, why does it insist on selecting this credit card BY DEFAULT every time I want to buy something?

Yours,

Outie

Update 2009-03-14: While it is possible to remove credit cards from the My Account section on xbox.com, this also failed for me. The reason for this apparently was that I bought my last 12-month Gold membership with it about a year ago. I assume – I HOPE – that Xbox Live would have noticed that the card is no longer valid and switched to the new card once the current membership expires. After manually re-selecting 12 Months Gold from the Membership Level menu on Xbox.com > My Account and “paying” for it with my new card (which will only happen once the current membership expires), I could remove the old card from my account.