PriceWaterhouseCoopers has handled the Oscar voting since 1934, and this was their one memorable mistake. So I'd give 'em a pass. That said, the partner is charge of handing out the envelopes might have been a little distracted, tweeting just minutes before the legendary mix-up.
Many of us, though, wondered why Warren Beatty and Faye Dunaway read the card at all if they were confused about it. Short answer... miscommunication. Warren Beatty was clearly confused about the card he'd been handed, so he hesitated and handed it to Faye Dunaway -- probably to see what she could make of it. Without hesitation, though, she read the name of the movie she saw. According to TMZ, this may have been due to some off-camera disagreement over who would make the big announcement. To me, it looked like Faye Dunaway simply thought Warren Beatty was goofing around.
Prediction: The PwC representatives will be told to leave their phones in the future. They won't be allowed to have them on their person.