And why would I choose that over Amazon Prime's pay-per-view services?
It'd be great if they had a subscription plan like Rdio or Spotify (similarly to Netflix), but it seems there are too many copyright and profitability issues involved.
I believe where iTunes differentiates itself from the streaming services is offline. The video you get is prefetched, so you don't need access to a large bandwidth pipe in order to view your content, and you can also store them on an iOS device or iPod and view the content anywhere. I'm not personally aware of other digital video services that work like this.
It'd be great if they had a subscription plan like Rdio or Spotify (similarly to Netflix), but it seems there are too many copyright and profitability issues involved.