[iand675]

I'm not entirely sure, but yesterday I observed some vending machines at a local university that worked with student IDs. The machines had a small antenna encased in the drink display, so presumably that model broadcast payment and/or inventory updates to some nearby receiver or via stock WiFi networks.

I'd expect that there would be a strong incentive to have the cards require network access to verify balances or else some enterprising hackers could potentially reverse engineer the process to add additional funds to the card.