Here is a list of players and what they have played on steam today lets add the numbers
Current Todays Peak
257,029 517,899 Dota 2
61,341 76,238 Counter-Strike: Global Offensive
56,067 62,756 The Elder Scrolls V: Skyrim
54,985 71,175 Team Fortress 2
46,660 50,333 Sid Meier's Civilization V
40,472 54,934 Football Manager 2014
32,327 35,128 Garry's Mod
25,022 28,235 Terraria
21,961 36,667 Counter-Strike
18,170 27,272 Counter-Strike: Source
17,844 18,808 Path of Exile
15,645 19,026 Total War: ROME II
14,302 16,360 Warframe
14,250 19,144 Football Manager 2013
14,220 15,350 XCOM: Enemy Unknown
13,443 16,216 Left 4 Dead 2
12,878 15,686 Assassin's Creed IV Black Flag
12,582 17,600 Call of Duty: Ghosts - Multiplayer
11,431 12,343 Borderlands 2
7,213 7,655 Dark Souls: Prepare to Die Edition
6,756 8,132 PAYDAY 2
6,732 8,635 War Thunder
6,405 11,615 Call of Duty: Black Ops II - Multiplayer
6,341 6,711 Fallout: New Vegas
6,306 6,441 State of Decay
6,234 6,972 Europa Universalis IV
5,931 7,093 PlanetSide 2
5,809 6,665 Arma 3
5,310 6,217 Arma 2: Operation Arrowhead
5,235 5,470 Kerbal Space Program
4,971 5,217 Rogue Legacy
4,862 6,829 Mount & Blade: Warband
4,809 9,665 Call of Duty: Modern Warfare 3 - Multiplayer
4,491 5,126 RIFT™
4,483 4,835 Crusader Kings II
4,423 5,771 Football Manager 2012
4,291 5,356 Empire: Total War
4,245 4,562 Infestation: Survivor Stories
4,153 4,209 BioShock Infinite
3,926 4,184 Game Dev Tycoon
3,806 4,247 Portal 2
3,646 3,861 Age of Empires II: HD Edition
3,640 4,538 Company of Heroes 2
3,540 4,481 No More Room in Hell
3,467 3,727 Killing Floor
3,409 3,865 Sleeping Dogs™
3,363 3,712 Don't Starve
3,331 6,691 Call of Duty: Modern Warfare 2 - Multiplayer
3,317 4,232 APB Reloaded
3,279 3,619 Prison Architect
3,252 3,703 The Binding of Isaac
3,208 3,739 Total War: SHOGUN 2
3,199 3,825 Might & Magic: Duel of Champions
3,041 3,163 Risk of Rain
3,041 3,110 FINAL FANTASY VII
3,030 3,334 Euro Truck Simulator 2
2,869 2,885 Saints Row IV
2,838 2,895 Dishonored
2,772 3,129 Batman: Arkham City GOTY
2,733 2,746 Marvel Heroes
2,710 2,938 Chivalry: Medieval Warfare
2,671 3,488 Stronghold Kingdoms
2,640 2,999 EVE Online
2,592 2,951 The Walking Dead
2,563 2,647 Torchlight II
2,546 3,145 Dead Island
2,507 2,674 Star Trek Online
2,452 2,913 Batman™: Arkham Origins
2,434 2,844 Farming Simulator 2013
2,413 2,865 Company of Heroes (New Steam Version)
2,405 2,546 Papers, Please
2,404 2,459 Contagion
2,312 2,412 Spelunky
2,288 2,456 Might & Magic: Heroes VI
2,112 2,337 Far Cry® 3
1,911 1,949 FTL: Faster Than Light
1,900 2,496 X Rebirth
1,877 2,000 Magic 2014
1,828 2,129 The Lord of the Rings Online™
1,814 1,839 Trine 2
1,785 1,952 Baldur's Gate: Enhanced Edition
1,783 2,696 RAGE
1,737 2,472 Napoleon: Total War
1,723 1,774 Half-Life 2
1,722 2,031 Saints Row: The Third
1,645 2,423 Call of Duty: Ghosts
1,641 2,087 Rising Storm/Red Orchestra 2 Multiplayer
1,621 2,121 Grand Theft Auto IV
1,600 1,801 The Incredible Adventures of Van Helsing
1,560 2,539 Call of Duty: Black Ops - Multiplayer
1,553 1,761 Dungeon Defenders
1,553 1,739 Batman: Arkham Asylum GOTY Edition
1,544 1,694 Assassin’s Creed® III
1,530 1,587 The Sims(TM) 3
1,451 2,152 Train Simulator 2014
1,420 1,751 Rocksmith 2014
1,408 1,471 DC Universe Online
1,371 2,150 Panzar
1,363 1,373 Surgeon Simulator 2013
1,332 1,728 Counter-Strike: Condition Zero
You take 7% of the current users that's till a lot of xp users, and 9/10 of the top 10 games can still be played on XP.
Also
http://news.softpedia.com/news/Microsoft-Concerned-with-the-Number-of-PCs-Still-Running-Windows-XP-397538.shtml“We estimate that up to 377,000 PCs in New Zealand... "377K and that's in New Zealand alone