That's interesting, I didn't really think about it until you mentioned it but they _must_ making a lot of money.

I couldn't find any specific rumors or estimates that are more recent than 2011. I did find a VentureBeat article from Jan 22 2014 that said that Dota 2 made $80 M and TF2 made almost double that at $139 M in 2013.[1]

Pricewaterhouse Coopers "Global entertainment and media outlook: 2013 - 2017" estimates that globally "entertainment and media" will grow at a compound annual growth rate of 5.6% over the next five years.[2]

So, even if you assume that they won't release Left4Dead 3, Half Life 3, etc over the next few years, just from Dota2 and TF2 alone their revenue for 2014 is likely to be more than $230 M. And that's a bare minimum guess. It's likely to be much more than that. But that's the lower bound of the estimate I guess.

Not bad.

[1] http://venturebeat.com/2014/01/22/doat-2-made-around-80-mill... [2] https://www.pwc.com/gx/en/global-entertainment-media-outlook...