I just submitted feedback to Apple on this matter.
Ever rented a movie off of iTunes? There is a chance scenes were missing from the film. For instance, some of the Star Trek films have scenes missing, and important ones too. Another example: Bad Lieutenant (2 powerful scenes gone entirely).
I have seen other people complaining about this in relation to other films too. Until they stop doing this, I won't be renting from them anymore. You will never know what scenes are missing unless you have seen the film before through a trusted medium, or another review alerts you to whether scenes have been deleted.
So you pay first, then watch, and hopefully nothing is missing, but with iTunes, many many movies have deleted scenes.