If you read on the Google wallet site, it tells you that you can use Google Wallet in the play store. Either that or I didn't quite grasp what it is saying....
google checkout was ultimately changed to google wallet. You can enter any credit card you would like just like any other online payment method.
Think of it this way, google wallet has two parts to it.
1) online payments, any card can be used
2) NFC point of contact payments, only citi + prepaid cards work using wallet app.