In Google Wallet, you can have multiple credit cards in your "wallet" and select which one you want to use for a payment.

The real problem with present-day NFC payment protocols is that they're really, really dumb from a security perspective -- sending your credit card number in cleartext over the air. In the future, they could implement something much better of course, but right now... dumb.

I suspect that Apple has stayed out of it because everybody wants a cut. The carriers want one system. A consortium of major retailers want another system. Google's doing their thing. Etc. It's a giant mess, with everybody angling to own a small percentage of overhead on a giant flow of cash.