Why do businesses prefer iPads and iPhones over Android devices for retail and event-based payment processing?

From an outside the US perspective:

1. Innovation on the mobile sector is predominantly attributed to the iPhone/iPad environments (read: Apple). Users dismiss (wrongly so) the marketplace size and potential of the Android ecosystem.
2. Android devices are not really catching up as a iPhone (smartphone) alternative to the masses. With companies like Huwaei , ZTG, Samsung, Nokia, etc. all rolling out cheaper models.
3. As Chris Cunningham says spot on, standardization is a huge issue.
4. For any one starting out to get an app out, for an online or mobile payment solution the question is do you make it for the iPhone/iPad first or Android or both? Not very many start-ups have the resources to make it for Apple + Android platforms. Most bet on the Apple horse! Look at Quora app (available first for the Apple ecosystem and then for the Android). I can cite very many other examples of the same follow the leader analogy.
5. To make retail and payment apps, I believe the Android platform is more pragmatic, conforming, affordable and holds the most potential for developers (especially outside the US, where Apple is not officially launched/supported, etc.)

I believe it is a mind-set issue on the whole to tap into the Apple environment first before Android.