The movie theatres are upset about how quickly DVD are coming out.  Some theatre chains even refuse to show some of Mark Cuban's films because he releases them to the theatres and dvd at the same time.  Now Disney suggests it would like to release DVDs sooner after their theatrical releases as welll
So the question is, if DVDs came out a month after the movie came out in theatre would you still go see the movie? Would you just wait for the DVD? Would you be more likely to buy the DVD after you saw the movie in the theatre? I think I would be just as likely to see the movie in theatre (I don't see a lot of movies in the theatre as it is. When I do, it is as an evening out more so than a desire to see a specific movie), and if I really liked the movie I think there is a greater chance I would buy the dvd afterwards. Don't under estimate the honeymoon period when it is in full force. 8 months after I saw an amazing movie, it no longer interests me, so I'm a lot less likely to buy the DVD.