Morgan Stanley has been digging into the active, spending user bases of some of the world’s biggest digital entertainment and e-commerce companies, cross-referencing registered users with revenues. It won’t be a surprise to see Apple topping the list: 500m iTunes users with registered credit cards – an account base that grew 55% in 2012. Apple is generating an average of $329 per user (clearly this is hardware, not just content spending), ahead of the $305-per-user that Amazon makes from its 200m registered accounts. eBay ($125 per user / 112m accounts) and Netflix ($123 / 29m) are next in the rankings. Music isn’t included, but if Spotify hits its $500m rightsholder payouts target in 2013 (which hints at around $715m of revenues for the year), that would be around $30 per active user, although the difference to Netflix is that Spotify has a free ad-supported tier. Anyway, Morgan Stanley is more concerned with Apple’s iRadio prospects, predicting that if 40% of Apple’s current users adopt the new service, even at $4.42 of revenue per user (which is what Pandora made in 2012), iRadio could be an $883m-a-year business for Apple.