I noticed this growing trend with me ever since I built my PC. Every time a game goes on sale, or Steam is having one of their major sales event then I will buy game just for the sake of having them on my list. I am fully aware I will never play them or ever get around to playing but it's just gives me a warm feeling knowing that they are on my list.
Are you also a victim of this addiction? Maybe there's a support group in my area for Steam addicts.