Scott Buscemi, 9to5Mac:
For those with boxed/retail versions of iWork, Apple is slowly rolling out the ability to upgrade for free. Keep checking your “Updates” tab in the Mac App Store.
Apple’s own apps are allowed to crossgrade. Non-App Store apps are allowed to upgrade to App Store equivalents for free, with no end-user hassles. Think that functionality is available to third-party developers who would like it? (Hint: no.)