Direct distribution to iTunes, YouTube, or Vimeo is really the dream of independent distribution. Cutting away as many leeching layers between the content creator and the distribution platform.
As Seanus says, (presuming it would be the same deal as the appStore) a 70/30 split on sales/rentals is WAY better than any deal you're going to get with a distributor today.
The issue for Apple is of course one of liability. As labyrinth as it is, the film production industry is built on protecting it's own butt. That means all the way thru things like contracts, insurance, ownership and copyright have been double and triple checked by teams of lawyers.
In a direct-to-iTunes distribution model- where's the assurances on Apple's part that the movie you've uploaded is yours, and contains no copyrighted images, music, or anything else that has to be cleared? Even if Apple had a team of people watching every film, how could they guarantee they'd catch everything?
And assuming a film is found to be breaking some copyright- who takes the blame? Could Apple guarantee that no one would come after them?
Then there's the issue of rating. Would all indecent films have to be screen by people at Apple who give it a rating? Or would all independent films have to be released unrated.
It's a really sticky scenario once money starts changing hands for the final product.
But the idea that someone could shoot a great comedy or drama for $50K and have access to the entire base of iTunes users; where they could potentially profit tens of millions of dollars or more. It's the goal we should be striving for- but there are lots of complexities along the way.