Stardock have released its 2009 Customer Report
in which Brad Wardell, President & CEO states that Steam "enjoys approximately 70% of the overall digital distribution market with their own Impulse at 10% and all others combined at 20%".
He puts the success of Steam and Impulse down to exclusive content such as Left 4 Dead, Half-Life, Sins of a Solar Empire and Demigod.
He also echoes recent comments about Steam's DRM status by stating "once a game requires Steamworks, it is effectively cut off from us, which limits our content." and the challenge they have with this means that "The problem is that it is not practical for us to install a game that in turn requires the installation of a competitorís store and platform in order to play it."