Slain Back From Hell, but Gone for Good?

Josh Griffiths writes: "This minty fresh new version is called Slain: Back from Hell, and has replaced the original Slain! on Steam. Public opinion regarding the game is higher since the latest patch, and it likely helps that this update was free. However, this brings up an interesting question. Is it okay for a developer to force their customers into getting a new version of their product?"