Worry not friend. Take a look on the OMNY FAQ. The roll-out of OMNY includes physical cards which are currently available from retailers as you mention, however, as MetroCards are phased out they will bring online new machines which dispense OMNY cards. They will work the same whereby you can pay cash or credit card. It'd be illogical to remove MC machines, no one wants to "have" to go to CVS to buy their card and reload it manually at a cashier, it's just that they wanted to get physical OMNY cards into the public hands a bit sooner before the machines are ready.