One stat in here supports a third, slightly different statement. The median player has not played 51% of their games, so: "most people who buy games on steam have not played most of the games they own."
Edit: You may not want to know if your steam account is old enough to drink...
but usually I'm buying the bundle for one or two things, and the rest is just window dressing. maybe I'll get to em, maybe not...
(I'll get to you someday, Mass Effect)