A few days ago there were rumours circulating regarding the fact that Valve was planning on adding a function on Steam that allows players to use BitCoin to make their purchases. Today the announcement was made official on BitPay's website, which announced a partnership with Valve's platform, allowing people to purchase content via Bitcoin instead of paying by credit cards or Paypal.
The choice of using BitCoin stems from Valve wanting to encourage purchases in emerging countries such as Brazil, India and China, where Bitcoins are very popular, and where people are often reluctant to buy with credit cards due to unfavourable foreign exchange rates or for fear of being cheated.