Some of these seem pretty logical; stuff that's removed from Steam maintains its registry entries, for re-download purposes and so stuff like the box art in the client is kept behind the scenes after the thing is removed.
Other weird stuff.
Civ V - Frankenstein
TERA (was on Steam then removed)
The Banner Saga: Factions (Kickstarter game)
[CONSOLE] Half-Life 2 Multiplayer
Dota 2 DLC Range
Age of Conan
Seven Souls Online
Crysis 2 GOTY
Saints Row IV (wat)
World of Tanks
We know Skullgirls is getting a PC port.