I wonder how much the illegality of it figures into the convenience. The study implies that copying, as currently practiced, has only a limited impact. But that takes place in a world where copying is illegal: people are repeatedly told that it's a bad thing (ad nauseam; I really don't need to be reminded every time I play my legally purchased movie) and the news is full of horror stories of people being harassed by prosecutors when they do get caught.
So I don't know what policy conclusions we could draw from this study. If we made sharing legal, how much would that impact people? Would they continue to want to go to the theater, which has a much larger screen and great sound, but which also costs a fair bit (and even more for any snacks you want, which are actually the theater's primary profit center) and which isn't as convenient in either time or space as having it at home?
I'm not sure how we could guess, aside from actually doing an experiment in which sharing was made legal, and even that is difficult to control (since the entire marketing process would need to change to accommodate it, and it's hard to predict which movies would have been blockbusters at the box office.)