Calling it a DLC though, like I said, is a little inaccurate. It could be sold as a stand alone game. DLC in the Witcher was free. DLC and Expansions cost money in games like Dragon Age and Bethesda games. DLC, to me, is the nickle and dime, 5-10$, that have little quality but make users feel their game is now incomplete if they don't purchase the content.
Infamous: First Light was actually sold separately from Infamous: Second Son where you never had to play the original game.
Edit: I would call the 18+ content in VNs to be Nickle and Dime type DLC. Someone previously posted that in Japan they don't even release 2 versions.