Apple has specifically CHOSEN to not have a file system like other systems. It's not that they're lazy or can't do it - they have CHOSE to not do it. Apple envisions a future where people have single purpose files which only one application uses, and store those files within that application. This is a LOT easier for the masses to understand.
It's just like Apple not putting in a CD/DVD drive into a MacBook Air. It's not that they CAN'T do it, but they want to push people to use the Cloud.
I know that they can do it.
Not providing file explorer for ios was reasonable because
-> a phone is not a document management system, you have apps, you synch your documents with the apps, finished.
-> it is more secure, apps cannot access documents from other apps. Great.
as long as ios is a pure companion device, not having a file management system is perfect.
But on one hand, the times are changing. Tablets REPLACE pc's. They are not longer just a companion, they want to be more. The way how microsoft tries to fullfill this is windows 8 (wich i think is done badly if you want to bridge the gap)
And the document center would NOT necessarily replace the companion stuff, it would just be an addon like gamecenter.
The documents ARE stored in the different apps, ready for sync with icloud.
But it would be also an public interface usable by other apps to access them ... just like email would need it.
See photos, photos have a public pick ui, the document center would by like a photoviewer / pick ui not just for photos but for documents.
I don't think it is something that would be contrary to the current way how its handled.
There is to consider that the "no filebrowser" decision was made for ios on phones where it makes perfect sense.
For tablets wich are replacing notebooks it makes less sense.