Prometheus director Ridley Scott has revealed (in this interview with Collider) that a good 20-30 minutes of footage was cut from the film for its theatrical release and that he intends to restore it for a longer DVD and Blu-ray cut - something he's done for many of his Fox films in recent years.
That's a lot
of deleted scenes. Why would he restore it for the Blu-ray coming out in less than 6 months later? Is it a cheap marketing ploy or since it was an "R" rated release were there many things the producer's didn't want in the theatrical cut?
I haven't seen it yet and am posting based on speculation and not with spoilers.
I'm sure the audio commentary would say why.