The situation is different here:
-4K raw scan and remastering done with film grain by James Cameron's production company Lightstorm Entertainment (Geoff Burdick supervised the restoration).
-Final color grading appoved by colorist Skip Kimball, director James Cameron and director of photography...
I don't think they added fake grain on "Titanic".
It seems to me, they made a perfect new 4K transfer and then moved to 3D convertion and degrained the film in this process. That makes a lot more sense for preservation, when you have a perfect new transfer with grain intact.
They degrained and...