I'm not gonna name names, but someone just mentioned paying for weed with a Square account. It'd be equally easy to use Paypal, Venmo, Bitcoin (RIP) or any of the myriad mobile payment systems that allow you to send money from your phone.
Five of the 20 best-selling casual game apps in Android's Marketplace involve illegal drugs. Virtual illegal drugs, of course! Guess how many are available for the iPhone? Yep, zero.