I'm more inclined to say that Steam makes additional DRM redundant, or perhaps irrelevant. Treating Steam as something unlike DRM, when it does perform the task of ensuring you have the 'right' to use content, is flimsier ground than I'd personally prefer to stand upon. That said, kudos to Valve for pursuing the agenda many companies seem to miss: use your online platform in a way that makes the product more valuable, instead of less, than the pirated version.