Kind of curious about that myself. From what I can tell there aren't any NFC options on the phone either so it could be something AT&T is limiting. Maybe someone with more knowledge can chime in..
It requires a secure SIM, which requires carrier support. AT&T (along with T-Mobile and Verizon) supports ISIS, which is their own mobile payment system that they created. I think WP8 will support ISIS, but ISIS is still in the testing stage right now. We probably won't get NFC payment until next year.