New Vegas 308k units sold on steam in October ?

[Zlejedi]

I have found interesting article in gamasutra which has top 10 sales numbers for steam games:

Estimated Top 10 Titles & Expansionsfor October 2010, by Units Sold:

1. Fallout: New Vegas (Bethesda Softworks) - 308,000 Units ($49.99)
2. Call of Duty: Modern Warfare 2 - Resurgence Pack (Activision) - 228,000 Units ($7.49)
3. Left 4 Dead 2 (Valve) - 178,000 Units ($15.00)
4. Counter-Strike* (Valve) - 114,000 Units ($9.99)
5. Half-Life 2: Deathmatch* (Valve) - 78,000 Units ($4.99)
6. DogFighter (Dark Water Studios, Ltd) - 67,000 Units ($1.50)
7. Frontlines: Fuel of War (THQ) - 53,000 Units ($2.99)
8. Medal of Honor (Electronic Arts) - 52,000 Units ($59.99)
9. Civilization V (2K Games) - 51,000 Units ($49.99)
10. Half-Life (Valve) - 48,000 Units ($4.99)

http://www.gamasutra.com/view/pressreleases/65722/Fallout_New_Vegas_Leads_Digital_PC_Sales.php

I wonder how much royalties does steam take for publishing games there ?

PS. It's crazy that they sold 50k HL1, 115k CS and 78k HL 2 so many years after release