Actually, there is much evidence. The Google Play Store is significantly less stringent on Android than iOS. For example, Google is estimated to get less than 1/10th the data from an iOS user as an Android user. The Play Store also, currently, doesn't effectively enforce the use of Google In-App-Purchase.
Because of that, there are less reasons to sideload away from the Play Store (from a company's perspective) as there are on iOS.
