I didn't bother to read the article obviously, but to compare opening weekend results directly with CAM downloads ignores many aspects. The most obvious to me is the people who did NOT go out to the theatre and who WILL NOT download the CAM, but who WILL wait two months for a high-quality free Blu-Ray rip to appear online. These are potentially lost sales for the theatres.
(Having said that, after going back to a theatre for the first time in a couple years specifically to see Avengers, I still believe the root of their problem does not lie with piracy, it lies with the appalling rudeness found in your average public gathering. For the same price, two months later, my living room is infinitely more comfortable and better equipped to show ME the movie in a manner I will enjoy and not be distracted by phones, screaming children, and poor sound).