How Apple could speed up iOS updates of core iOS apps

As of today, Apple delivers the basic core iOS experience with iOS builtin default apps. They are updated at each major iOS releases which happens basically every year. Some people think it takes too long to get improved iOS features. I tend to agree.
Besides default apps, Apple currently offers a few more apps like Remote, iTunes U, Podcasts, Find Friends that are made available on the App Store. These apps aren’t part of the default core experience of iOS. Apple’s reasons to keep them apart from the core apps can be guessed. My question is: why not use the App Store in order to push more frequent updates to core iOS apps?
What Apple could do with iOS 7 is to introduce the concept of mandatory updates that would me made available through the App Store and would target all default iOS apps. This way, an app like Mail could receive new features and fixes much more frequently without having to wait for the next major iOS release.
By pushing mandatory updates to core iOS apps, Apple could evolve the iOS experience at a faster pace and mitigate the perception of falling behind others…