I think that Apple's 17.1% share of the mobile market is too small for it to make a world shaking difference. For this to really take off, it would have to be inter-platform.

Edited to add: From that same link it could be argued that Apple's iOS share of 34.3% is more relevant. Older devices that can't support the latest iOS with Passbook aside, I'll concede that. I still stand by my assessment that the share of Passbook capable devices isn't enough to dictate a standard on their own.