Electronic Arts has not released certain titles on Valve’s Steam service since launching their download service Origin. Not surprisingly, Mass Effect 3 is joining the ranks of Dragon Age II and Crysis 2 in games from EA that aren’t coming to Steam.
“During initial release Mass Effect 3 will be available on Origin and a number of other 3rd party digital retailers, but not on Steam at this time,” said BioWare. “Steam has adopted a set of restrictive terms of service which limit how developers interact with customers to deliver patches and other downloadable content. We are intent on providing Mass Effect to players with the best possible experience no matter where they purchase or play their game, and are happy to partner with any download service that does not restrict our ability to connect directly with our consumers.”
Source: social.bioware.com