Well, if I'd be getting a PS4 I might get it for these games, but the main reason would be Kingdom Hearts games (most of them are also on PS3, but KH2.8 and the soon-to-release KHIII are PS4 games.) They'll never get released on PC and I love how awesome and convoluted the story is.
But I think Horizon Zero can be considered the main reason to get PS4, currenlty I'm just a PC gamer with a lower end PC so I can't get much into this.
I mentioned this post in my Daily Picks if you'd like to check it out.