The pool of Android users is so varied it's difficult to categorize them anymore. I wonder if iOS users are just more comfortable purchasing stuff online? Most iOS users I know have purchased music, apps and video on the iPhone or iPad. They are comfortable with their phones and iTunes and the App Store are a major reason for that confidence. What others see as Apple's iron fist, customer see as Apple looking out for them.
A few friends have tried to download a popular game from Google Play only to find out they bought a knock-off. If you're been burned even once you're probably less likely to feel comfortable buying anything with your phone, even when it's perfectly safe to do so