I think, it's perhaps the too much gore concept and not enought Next Gen models for an FPS game that make them not to publish it !
For Steam i think it's caus it's an FPS !
You can find on Steam very very little price lot more good , long and better FPS : Painkiller for example !
Far Cry , must be very little price also, and the horror
theme is lot more better used in L4Dead with it's multiplayer not only gore effects everywhere!
FPS games are not that casual but more core gamers , and if you target PC games not iphone, I think if you go FPS for steam, you must have something speacial, special ideas !
Mirror Edge, Portal game for example !
In Indie games you won't find lot of FPS games !
Or they are special, not a simple shoot with lot of gore !
Take example on Penumbra game : FPS/adventure with it's own
Advanced engine and physics !
Well just my opinion on Steam and FPS games