Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Actually, when Apple introduced Ping in iTunes 10 it appeared on the phone after the first sync with iTunes. It didn't happen through the App Store at all so it's quite possible to update core apps silently.
 
the app store/itunes app basically display a server generated html page, so any content in those can be updated dynamically.

all other apps are in the non writable main firmware, so they can not be updated at all without itunes doing a firmware update. One of the things jailbreaking does is make the main firmware partition writable.
 
I doubt Apple makes that many meaningful changes to the core apps. Most of them are extremely stale. Besides, making you upgrade your firmware to get whatever changes are actually made to the core apps is a great way for them to combat jailbreaking.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.