Good Old Games Interview, The Witcher 2 Pirated Millions of Times?

Their Good Old Games service and strong stance against DRM are not the only the topics covered in a new interview with CD Projekt's Marcin Iwinski on PC Gamer, as the CEO and co-founder even speculates that several million illegal copies of The Witcher 2: Assassins of Kings were pirated during the game's first couple months of availability.
PCG: Can you offer any concrete numbers or percentages as far as Witcher 2 piracy goes?

MI: There are no stats available, but let's make a quick calculation. I was checking regularly the number of concurrent downloads on torrent aggregating sites, and for the first 6-8 weeks there was around 20-30k ppl downloading it at the same time. Let's take 20k as the average and let's take 6 weeks. The game is 14GB, so let's assume that on an average not-too-fast connection it will be 6 hours of download. 6 weeks is 56 days, which equals to 1344 hours; and with 6h of average download time to get the game it would give us 224 downloads, then let's multiply it by 20k simultaneous downloaders.

The result is roughly 4.5 million illegal downloads. This is only an estimation, and I would say that's rather on the optimistic side of things; as of today we have sold over 1M legal copies, so having only 4.5-5 illegal copies for each legal one would be not a bad ratio. The reality is probably way worse.
There are a couple of assumptions in there, but I suppose it's not that far-fetched. I wonder how piracy of the PC version will compare to piracy of the Xbox 360 version next year.