Valve basically crowdfunded their tournament prize pool. They started out by offering an initial $1.6M prize pool, but gave every dota 2 player the option of buying a "compendium" for $10, and each compendium increases the prize pool by $2.50. That means Valve makes $7.50 per compendium sold.
I just ran the math, and as of right now there have been ($3,365,563 - $1,600,000)/$2.50 = 706,255 compendiums purchased. Since Valve earns $7.50 per compendium, that means they just made $5.3M in a couple days. And they're set to make even more next year, since the Dota 2 playerbase has some nice exponential growth: http://steamgraph.net/index.php?action=graph&appid=570&from=...
I'm not sure there are any articles about this yet, because this news is so new. I wish I had a decent article to submit to HN instead of this link. But this is certainly newsworthy, so it's a matter of time before you start hearing other news sources talking about it.
EDIT: If you're looking to see what a Dota tournament is like, here are two great matches from last year:
Game 1 https://www.youtube.com/watch?v=OaGSi1YTA-E
Game 3 https://www.youtube.com/watch?v=ajQuCZx-yx8
The production quality is so good!
EDIT2: Also, Valve made a movie called "Free to Play" which documents what life is like for top-tier Dota players: http://www.youtube.com/watch?v=UjZYMI1zB9s