Dragon Age II recently expanded with Legacy, but the expansion can only be bought in-game, not via online stores such as Steam. No big deal, you may say, but this is in violation of the rules and regulations of Steam. Accordingly, Dragon Age II, has been removed from Steam.
Obviously, EA and Bioware, are hoping to cut out the middle man by offering expansions and DLC exclusively through in-game sales, but Valve are having none of it. How this affects the longterm relations between EA and Valve remains to be seen. EA have been publishing Valve's products through the EA Partners programme, and many a big title from EA has sold well through Valve's Steam service. There has also been rumblings that Battlefield 3 will not be sold on Steam, and everyone is anxious to see how Bioware's next big title - Star Wars: The Old Republic will be treated on the service.