Ah I was thinking this had happened but I kept seeing it in my games list and on Steam player stats. I was going to uninstall it because I didn't play it much after initial few days, and need HD space. I guess it decided for me. I wonder if it deleted all of the files?
edit: It didn't. Had to use Add/Remove which launched a Steam window to confirm deletion. Of course, now it's like Day of Defeat: Source which I recently removed. Clicking Steam games from Add/Remove just brought me to Steam. So I deleted files from Steam but the entry is left in Add/Remove. With L4D2 demo, it actually brought up a Steam window, but it still left the entry in Add/Remove. I don't know why that's not been fixed.