The iPhone OS completely removes the concept of a “file.” It promotes apps to being the primary level of user interaction, and it stores related things inside databases that are content-specific. When you pick up your iPhone and want to view photos, you open the Photos app, which connects to the photos database and shows you all of your photos. When you want to listen to music, you open the iPod app, which connects to the music database. Everything on the iPhone is task-centric, not file-centric. The “file” part of completing tasks is completely insulated from the user.
Not exactly true. Many apps on the iPhone like to keep the data to themselves. Apps like Layers can export to the camera roll, but if you want the layered file to use elsewhere you’ll have to email yourself a PSD. Also RjDj, like most apps, will let you share creations to the internet, but not with other apps.
I’ve been able to edit movies using multiple apps without leaving the phone, but it means exporting footage to the camera roll a few times and the quality suffers as a result.
The lack of a filesystem is the single greatest limitation to the usefulness of iOS.
Hopefully someone will think up a system that offers the best of both worlds. I’d love a Dropbox space that my phone could just dump data into, allowing apps to create standards for sharing the information they need.