a) Cable companies put the squeeze on content owners to give them exclusive rights
b) Netflix religiously clings on to both commercial-free and buffet-style pricing
It's tricky. You have a movie studio that pumps out AAA features that cost upwards of $200 Million to make, then Netflix comes along and says "hey, you mind taking this really low price for your content, hopefully in perpetuity?" What would your response be? So, it may be awhile before Netflix gets the big-budget blockbusters quickly. That is, unless, their subscriber base goes over 50 Million, then by ALL means game on.
I think that, in the interim, a dynamite move for Netflix would be to acquire a music streaming company like Pandora or Spotify, then a streaming game company like Galkai or OnLive. Push it out on a set top box, a la the OnLive console, charge $19.99/month with the opportunity to rent premium newly-released blockbuster movies, hot records, and AAA games on the day of release for the same prices that redbox or gamefly charges to rent them per day.