I probably buy fewer things through Steam than I do Humble Bundle, GoG, etc., but do all my gaming through Steam anyway just for all the other things it provides, even aside from social things like friends-lists and server joining.

To name a few: cloud saves, steam workshop, big picture, and steam controller.

Even if I dropped all the social features in favor of some other platform, I'd still be launching all my games through steam for those features alone.