Well, you need to see it at higher resolution. And it's not so much that you can see the grain on the actors (you really can't very well), but you *can* see it in the window frame, and it's *not* moving like real film grain should. It's just distracting to those who are familiar with the way film and film grain works.

Check out Ady's 720p ion cannon clip. You can see it plain as day there. (Though the planet curvature isn't fixed on that one, and the red light isn't there either.)

--EDIT--

Angel, you beat me to it :-)