[Amake]

Two things that could contribute to this trend: If a big name game gets good reviews, you know a lot of people are going to buy it, and that means the chances of finding a clean torrent and of finishing downloading it before running out of peers go up, and likely the speed with which you can download it too. So it's more convenient. And secondly, if you know a lot of people are buying a game your incentive to support the developers decrease. It's always easier to justify stealing from the rich.

PS. Would it have killed them to compare their figures to the sales of the games?

New Vegas: 5 000 000 sold (November 2010)
Darksiders: 1 200 000 sold (February 2010)
Need for Speed: >5 000 000 sold (February 2010) (Compare to projected 4.2 million sales)
NBA 2K11: >5 000 000 sold (May 2011)
TRON Evolution: 450 000 sold (First ten weeks)
CoD BLack Ops: 13 700 000 sold (March 2011) (US only)
Starcraft 2: 4 500 000 sold (December 2010)
Force Unleashed 2: 2 110 000 sold (First ten weeks)
Two Worlds II: >2 000 000 sold (February 2011)
The Sims 3 Late Night: 850 000 sold (First ten weeks)

That's just some scetchy-ass figures I pulled from Wikipedia and Gamrreview, but we see there's no immediate connection between sales and piracy. I don't know what conclusions to draw from that other than "Those big name developers sure are bitching a lot about selling millions of games and also Tron Evolution sucks."