Apple worried for getting sued for 3rd party app content
techradar.com
techradar.com
By not approving games ourselves (in fact, Microsoft employees are banned from even looking at un-reviewed games), we achieve some sort of legal protections (which I lack the vocabulary to describe).
This process also scales better than a central review board model. Indie Games doesn't need that scale yet, but the back-end is generic enough to be used with other user created content which might demand the scale: http://creators.rockband.com/
If Apple is going to say that it is not responsible for content in iPhone applications then that could mean that the review process will have to be relaxed. And that the SDK agreement will have to be changed.
Because right now they do look in detail at content in applications and numerous apps have been rejected based on their usage of copyrighted content.
that is untrue, Apple doesn't care if you violate copyright. They consider the violated party to handle that deal. (example: there was a blatant ripoff of mario, it was not by nintendo and still made it on the appstore)
That would be my guess anyway. That said, hey, here's to hoping!
The device can download images and copyrighted content, apple can not control downloaded content so there's a nice out here.