Apparently the movie studios are placing further restrictions on rentals in order to promote the purchase of shiny disc. Marco Arment says this won’t work because:
If I’m adding a movie to my Netflix queue, I’ve already decided not to buy the DVD. I’m adding it because it looks mildly interesting and I’d like to watch it sometime.
I take the opposite approach. I am unlikely to buy a movie unless I have previously rented it. Why would I buy it if I don’t know whether or not I like it?