I'm just saying that the publishers balance potential lost sales due to DRM against potential gained sales because of DRM and see a net sales gain. It's a publicly traded company - they have an obligation to shareholders to address this.
Say that 5m copies have been downloaded illegally (I think that's pretty conservative in the case of AC2). Assume that a small percentage, maybe as low as 1%, of those that pirate it would actually buy it if they couldn't pirate it. That's 50000 copies. Realistically, how many people are put off from buying by this DRM. If that figure is less than 50000 and covers the development cost of the DRM then you have your net profit and DRM "works".
Adjust the figures to whatever you think is realistic, but
publishers have a lot of research data that they don't make public so they're probably in a good position to make predictions.
It doesn't mean that their numbers are correct though.