Tom Waits said:
Bigger sample size, more people are going to buy, more people are going to pirate.
Based on what? And don't reply with human nature because you've only spouted vaguely anecdotal points in this regard.
Why would most pirates go out and purchase a singleplayer game at full price after beating it?
That assumes that people get through the whole game before purchasing it. But I can think of a few reasons:
Patches for bugs being fixed.
Updates that add more to the game.
(As silly as this is) Achievements.
Appreciation for a job well done by the developers.
Buying the game so that a possible sequel is made.
What this a rhetorical question?
But they'll do it if there's multiplayers feature. Now what if they get rid of DRM, so now they can play online with a pirated copy, would pirates still go out and buy it?
You must not know how DRM works. Illegal copies of a PC game can't access the multiplayer servers of legit players. DRM or not. Try torrenting Diablo 2 and getting online.
How legit are those "studies"? It's like asking bunch of alcoholic if they have a drinking problem.
Since you're too proud or too stubborn to use Google or do any research yourself let me answer this and I'll try not to be smug.
"Norwegian School of Management has found that those who download music illegally are also 10 times more likely to pay for songs than those who don't."
http://www.guardian.co.uk/music/2009/apr/21/study-finds-pirates-buy-more-music
NPD study and Ofcom study (US and UK respectively) show similar results.-
http://www.techdirt.com/articles/20121126/00590921141/dear-riaa-pirates-buy-more-full-stop-deal-with-it.shtml
2 Dutch studies (Dutch Institution for Information Law and CentERdata) actually say that people who pirate games are 5 TIMES as likely to buy the game they pirate than people who don't.-
http://www.webpronews.com/pirates-more-likely-to-pay-for-digital-and-physical-media-than-non-pirates-2012-10
Now that's four different countries and 5 institutes that have thrown your anecdotal BS under a Mack truck and run over it while backing up just for good measure. Unless you can throw me some numbers that show the opposite and tell me how I'm wrong with data rather than the your "humans are dicks" Spidey-Sense, I'm afraid this case is closed my friend.
Like I said before, we can disagree but the numbers are heavily on my side. It'd be foolish to be so ignorant and ignore the information that I have presented.