If it makes you feel any better, I totally missed them too until I tried to figure out where the hell my "cursor" was on the screen. There's a little box in the top right corner ("up" got me there) that reads something like "It's better in 3D".
There are three 3D trailers on this disc (top right corner). They are full scenes from Titanic, I, Robot, and Avatar. The Titanic one is the opening scene from elder Kate Winslet through to when she gets out of the car on the docks. I, Robot is the scene where the large trailers of robots move...