Its the fact they just expanded into those regions... server numbers will grow throughout the year. Steam in the US is still a very young service being managed only by 27 people. When it started it only had 1 server.

Valve isnt a huge company, no one stated they were. They are the biggest on the DD front though.

There is also other DD platforms around the world too like D2D, StarDock, etc which need to be included into the big picture.

There is also the problem of how many people of some of those regions have broadband. I'm pretty sure Russia doesnt have many people with broadband yet.  Even the US failed to have a really good level of broadband users. While this number will grow pretty fast as infrastructure improves it still will take a few years.

Easy, there's 3 reasons why Halo 3 players probably have a much higher concurrent users:

1. Xbox 360 is a dedicated gaming machine. Meaning players won't get out of their games to see websites, work, etc...
2. Xbox 360 audience is younger. Means they have more free time than the more mature PC audience.
3. Xbox 360 has nowhere near the amount of competitive games that PC has. Which means Halo 3 doesn't have much competition from other FPS on X360.

I don't trust VGChartz when it comes to compare the PC version of games. About COD4, when Activision said that COD4 sold 7 millions on PC (Jan 25), 360 and PS3, when you add the VGC numbers of PS360 it comes out 6.5 millions (Up to Week 11), leaving only 500k to PC:

http://vgchartz.com/swlaunch.php?reg1=All&game1=Call+of+Duty+4%3A+Modern+Warfare+-+PS3&reg2=All&game2=Call+of+Duty+4%3A+Modern+Warfare+-+X360&reg3=All&game3=&weeks=50

I mean, the PC version of COD4 sold 383k in the US in November+December. So COD4 would have to sell only 117k in UK, France, Germany, Italy, Spain, Benelux and most of January in the US.

I just foud an article from Nielsen that says that the average COD4 PC player in 2008 only played 403mins (6.7 hours) per week, though it was taken from a very small sample of 1200 players: http://www.shacknews.com/onearticle.x/56580

EDIT: ignore taht bit about the graph. We would need to only include VGC's numbers from the markets said above in the graph, which isn't what it showed.

The current players playing at any given time can be misleading and does not reflex the amount of copies sold.

Look at CS:S at the moment they are 44k playing and at peak over 105,000 players playing at same time (00.46am UK time).  So I supect most of them 44k are from the americas at this moment in time.

If I could find a network card that vista 64 would actually like, I would jump all over L4D.

Halo 3 has easily over 100,000 players on at any given time. You can spin it however you want but 18,000 online is not a very good number. Also L4D was 3rd in the last xbox live top ten I saw so going off Halo 3 numbers which was second then the console version of L4D must have more players online than the PC version.