"I'm sure there are some people who are willing to buy a game if they can't pirate it but I doubt it's a huge number. Most people probably either fall into piracy only or buy only but we'll never get to know for sure."-Bluth54, neogaf http://www.neogaf.com/forum/showthread.php?t=1339781&page=2
Indeed, here's the thing. Unless someone has cash around and gamer friends pushing heavily for that particular title. There's plenty of legally free games of equal or superior quality. The complexity and graphics of low cost and even free games is increasing over time. You're competing against free and often superior products.
DRM cannot stop copying of digital data, it can only impede you playing a copy for a while. And as automated intelligent means of cracking are developed, systems that might be able to analyze at faster than human speed and see more complex patterns than humans can catch, expect any drm to be cracked within hours perhaps even minutes of release in the future.
I often buy a title on multiple platforms, even at full price. But if it has draconian drm, that can easily be up to half a dozen sales lost from me. I'll only buy one copy if that, and when it's sold at peanuts heavy discount, or I'll play something else.
Resident Evil 7, I was probably buying for xbox one, ps4, steam(and eventually on likely future android and ios), but now it'll be highly discounted on a single platform if that. If I can't find a disc, I might buy it again, but now that won't be the case either, I'll buy digital where it's linked to a platform at heavy discount on a single platform, if that.