The document compares the in-app purchasing strategies of the top 50 grossing apps to other freemium apps. It finds that the top apps have higher conversion rates, average selling prices, and average revenue per paying user due to strategies like engaging users early, making it easy for users to return, differentiating their in-app catalog, and designing in-app purchases into the core game experience. The top apps also have longer user sessions and retention through social features, adjustable difficulty levels, and catering to their best customers.