Same here. Maybe it was to counter the problem some people have with buying in game purchases and using the Google Wallet method of billing your carrier?
possibly. i spend a lil bit on one game in particular from time to time but it doesnt give a GW option..card or bill Sprint only..might even be for recovery if any problems pop up possibly..
Have you bought anything through say, the Play Store? Music, Movies, free or cost? If so, it uses the Google Wallet app to complete the transaction. I'm sure you have seen it, maybe just didn't realize it. But any games downloaded through the play store would also use the wallet to complete in app purchases. Its a requirement for being in the play store I believe.