It's funny how your proof is something that I already debunked and deconstructed: http://vgchartz.com/forum/thread.php?id=80037

Anyone that crossed with me knows that I believe Call of Duty 4 did humongously on PC. I think it reached/will reach 10 millions copies sold on PC, or come near it, not counting MAC sales. Of course most people here on the forums thinks I'm crazy because my only proof is that COD4 shows up quite often in the PC top sellers lists across the real and digital worlds. Even today it still shows up every now and then in places such as Steam and Direc2Drive.

In order to make you think there is a decent chance I'm right, I'll explain how different the PC gaming market is compared to Console market, and how PC games' sales are throughout time. Console games are very front-loaded, and the first month of a game usually makes up for the large majority of it's sales - A trend that is the complete opposite on PC games.
Historically, PC games sell only a fraction of their lifetime time sales in the first month, sometimes the initial month could make up less than 5% of lifetime sales. They have legs capable of keeping sales stable for years, and with the rise of digital distribution they no longer need to fight for shelf-space. However, PC games that are percieved as must-buys can still be sold at an honorable pace for 15 years or more, well after it's release and. Examples of such feat:

• Fallout, 1997. Still selling worldwide in bundled and budget editions, and is currently one of the top sellers of GOG.com.
• Starcraft, 1998. Sold "only" 1.5 millions in the first 9 months, now has over 11 millions sold.
• Curse of the Monkey Island, 1997. Several budget editions available, should soon come to Steam.
• Myst, 1993. Still in stores, bundled and budget editions. I bought "Myst - The Collection" last year.

As said before, digital distribution helps this trends of long legs, especially now that PC games have an unlimited supply and don't need to steal shelf-space from each other. This creates a harmony where the costumer doesn't have limited choices anymore. In 2007, Digital Distribution Revenue for PC games were about $2 Billions, while Retail was $3 Billions (a 2-to-3 ratio between Digital vs Retail sales).

Now onto the main question: What about Call of Duty 4? How did it do on PC?
I have always defended it sold much more than most think. In the beginning everytime I saw PC Top Sellers on Retail, there it was, COD4 selling better than World of Warcraft and Sims 2 in it's first few months, and even after a year it was still around the same pace as those juggernauts... but there was one big difference: COD4 was THE juggernaut in digital distribution, a market that both Blizzard and Maxis barely touched but big enough for indie developers to flourish and Popcap to crap gold nuggets. Infinity Ward's baby dominated Steam and Direct2Drive for months and  fiercely clashed with The Orange Box, Team Fortress 2 and Counter-Strike: Source for the top spot, often victorious.
Even now, after almost 2 years of it's release you still see it in the Top 10 Sellers on Impulse at 9th place, and 10th on Steam's Top 10 Selling Action Games (which puts the game in Steam's Top 20 Sellers).

It took Starcraft over 11 years to reach 11 millions sold, and some of you might think this: Then how the hell can you even believe COD4 would come near 10 millions in just 2 years?! There are several good reasons:

• The PC Gaming Market is much bigger than 11 years ago.
• Starcraft only sold 1.5 millions in it's first 9 months, and it never had a spike the size of COD4.
• Call of Duty 4 has the advantage of Digital Distribution.

Activision never released hard figures for the PC version of Call of Duty 4, but in early 2008 they told Call of Duty 4 had sold over 7 millions copies in 2007 (until December 31, 2007) on PC, Xbox 360 and PS3 combined. MAC and NDS sales weren't included. Those figures were taken from the Retail sales of just a few selected markets:

• North-America (USA + Canada)
• UK
• France
• Germany
• Italy
• Spain
• Benelux (Belgium + Netherlands + Luxembourg)

Incredible sales no doubt. Looking at these countries we find that most of them are console-centric markets (NA, UK, Italy, Spain) and only Germany, France and Benelux are more PC-focused, leaving out dozens of smaller PC-dominated countries like the eastern european coutries, scandivian markets, Portugal, China and South Korea, etc...

8 was the number of weeks that COD4 had been available in 2007, since November 6th in NA and 9th in Europe. According to VGChartz:

COD4's NA sales in 2007: 3,684,207
COD4's Others sales in 2007: 2,019,705

That comes to a total of 5,703,912 sales in 2007 for North-American and Others Regions. Nifty! There's a 1.3 millions discrepancy, so PC must've sold that much in the above markets, right? Wrong.

In VGChartz's North-American figures it's also included sales from Central and South-American markets. I happen to remember the great ioi once said that those sales account for around 5% of the Total NA sales, so let's remove that excess:

COD4 USA+CAN sales in 2007: 3,684,207 - 5% = 3,499,997

A nice, uneven number it is. Since COD4 came out in November 9th in Europe, so it was 3 days short of 8 full weeks. Let's believe those 3 days are around 30% of the Week 8 sales and take them out:

Others Sales - 30% of Week 8: 2,019,705 - 60,785 = 1,958,920

Now as you know, the Others regions aren't just Europe, but also Oceanian countries, Africa and Mainland Asia. Sure, Africa and Continental Asia don't count for much in console sales, but Oceania has Australia and New Zealand, and let's not forget about the dozens of european coutries that Activision failed to mention for it's 7 Million figure.
Now it's a matter estimating how much is the share of UK, Germany, Italy, France and Benelux combined is in the Others. Satoru Iwata, Ninty's Boss, claims that the U.K., Germany, France, and Spain represent 75-80% of the full European market for Handhelds. However, if it were the PC or Console sales only it would've a bit different, since PC has more popularity in many countries outside those, and I think handhelds are seen more as a luxury than consoles. Furthermore, VGChartz's Others include Australia, New Zealand, Asia and Africa. So let's think the countries Activision said is about 65% of Others:

Others - 35%: 1,958,920 - 685,622 = 1,273,298

In the end we get: 3,499,997 + 1,273,298 = 4,773,295

That means Call of Duty 4 sold slightly less than 4.8 millions copies on PS360 out of those 7 millions.

What does this mean? It means PC sold over 2.2 millions in a few countries, in less than 2 months and not even counting digital sales. If the Digital-to-Retail ratio were true then (we don't know), it would mean COD4 would've sold 66% more with the digital sales for a total of 3.7 millions in just 7 markets. But we don't know how digital sales are, so let's not touch this matter again.

When you think about it, Starcraft 1 sold 1.5 millions in 9 months WORLDWIDE, while COD4 sold 2.2 millions in only 7 markets, not counting the Eastern European countries, Scandinavian countries, Russia, South Korea, Australia/New Zealand, etc... and we certainly couldn't see how those legs performed, although it still was one of the best PC sellers in 2008, Retail and Digital, and still selling in 2009.

http://www.gamespot.com/news/6185154.html