The fact they need rules to enforce use of their inferior payment system shows how inherently anti-competitive IAP is. If it were optional and you could freely roll your own purchase mechanism, most (not all) developers would remove Apple IAP with the current 30% fees.
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.
