Wow, this is some thread!
Just want to throw this nugget out there, the OP asked "why do owners of high end PC's pirate games", we can assume someone who can drop $2-3k building a computer would have more than enough to pay for games right?
The answer is always, because they can. Because why should I pay for something I can get for free?
Many people don't understand the microcosm this place displays (or other groups/blogs/etc) of people who say they download pirated copies, if they like the game they buy it. In the end you are a fraction of a percentage of people who pirate games. Everyone else, not only couldn't give a hoot to post on a message board about it, downloads them because they are free.
I know this because at almost 35 years of age I've gone through many years of gaming. When I was a kid I pirated games, mostly because my buddy was like "hey you want this copy of Strike Commander"? Sure dude why not! Then I went to college for Computer Science, grew a conscience, and since I do not pirate anything at all. But to the rest of the world, if it fell off the back of the truck, I guess its mine, and pirate sites that have this stuff ready to download, well thats the truck with the open door. It happens with everything, its amazing how many people will take something for free because its there, even though its technically not theirs. But they aren't like holding up a store at gunpoint, so therefore its ok.
My sister's fiancee makes more money than I do, owns multiple cell phones, tablets, laptops, video game consoles, etc, and pirates EVERYTHING, music, movies, games, it doesn't matter. Not only that he took my moms phone, rooted it and installs this pirate crap and tells her "why pay when you get for free, its ok!". I deleted that off of it. And all his friends are the same, and tons of other people I know. I do a system build or a network setup and they balk at having to pay for Microsoft Office licenses. "What you can't just give it to me?" because their buddy installed a pirated copy of Office 97 on their old Pentium, its normal to them.
People don't see the value in paying $50 (or whatever for software) because it is out there for free, or there was so many years of getting it for free its expected. Any other excuse is BS, yeah you may proselytize about broken games, or trying before you buy, but the truth is there are so very few of you in existence. You aren't as much of the problem as the base culture of "why pay when I can get it for free"?