Actually aren't there other hybrid dinos? Perhaps the trailer is only hinting at the first publicly announced hybrid while keeping the iRex a secret in the movie. In some toy material releases there is a stegosaurus triceratops mutant for example.
Also I know a lot of people that hate the San Diego attack but I mean come on, it was the logical next step. First you create dinosaurs, then you show the viewer why creating dinosaurs was a really bad idea. As an added plus we got to see what a T-Rex could accomplish if set free on city streets. JPIII... I'm not sure what the point of that was except to piss on the T-Rex.