This is an interesting calculation, Research2Guidance has published a report that features a chart which illustrates the comparison of average downloads per app on a number of platforms to iOS. Looking at that chart above, you can see that OVI Store (Symbian) has +160% more downloads per app on average than iOS, while Windows Phone comes second in at +80%.
Surprisingly, BlackBerry came in third at +43%. Many users on competitor platforms may complain and make remarks about the amount of apps available to WP users, but we sure have quality over quantity and it goes to show with the amount of downloads apps are accumulating. Check out our article covering Marketplace statistics and case study for more insight on WP.