How does this differ from, say, MochiAds, GarageGames, WildTangent, Steam, XBox Live Marketplace, or the iPhone App Store? (not to be critical, just curious)
ed: to clarify, the only reason to have any portal is to promote the app.
ed2: I should have just linked to this in the first place: http://ludamix.blogspot.com/2009/01/intro.html