Well, for one, file management...
Umm, the iPhone OS does have a file system. What makes you think a more general purpose tablet wouldn't add a file management app that lets you copy files back and forth, save your attachments, etc and view them with your local apps?
The only restriction for apps in the current OS is you cant access a different folder than the one an app is installed in... but thats a security model limitation; that could easily change to allow a Documents folder or what not.