What about “roll your own” equates to google wallet? That’s very much not roll your own, and not what the grandparent was arguing.

You misunderstand. The customer can use Google Wallet if he wishes.

On the Web, payments almost always go through the credit card system, using one of many payment providers (PayPal, Stripe, etc.) set up by the seller. The customer also has the option of using a "safer" virtual credit card to avoid the possibility of credit card theft.