I agree. iOS needs some way to share files amongst applications. If I create a document in Pages or Numbers or Keynote or some third party application why can't I easily see it in iBooks or Goodreader, just for example.
I somehow think that Apple doesn't want this. They want to say that you have books and photos and videos and music and presentations and spread sheets and they all live in separate applications so you don't need to share them.
That philosophy led them to come up with the media tabs in the inspectors in Keynote and Pages and Numbers and iMovie. They hide the file system and give you access to what they think you need. This is convenient, but incomplete. What if I need something non-standard? What if I want to drag in some text I took as notes in a third party program to use in a Keynote presentation. I have to use cut and paste as there is no way to find a .txt file from Keynote.
Kudos to Apple for trying to think around the file system, but they need to give us access to our data somehow.