The trailer features a generous helping of Robert Downey Jr. as sardonic arms dealer turned armored-warrior Tony Stark, glimpses of his armor and an impressive sequence where Iron Man flies, outracing fighter jets.

The sequence had to generate buzz, since that's the only reason it exists.

A spokesman for Industrial Light & Magicconfirms that the flying Iron Man shots are not "finals" (completed, delivered visual effects) and were only made for the film's Comic-Con promo reel. The real flying f/x are still being created.

There's a tradition of creating material just for the trailer: Savvy scribes have long known that some scenes they write are likely to be in the trailer but not make it into the final cut.

One wag says he's often asked to write what he calls the "So Far" scene, where the lead might tell his best buddy, "So far, I've built a suit of armor that makes me a superhero, but I'm spending so much time fighting crime my girlfriend thinks I'm cheating on her."

Development execs like such scenes: They're useful in the trailer and superfluous in the film. But advance promotional shots are a bigger headache for visual f/x companies. Trailers have to go out months ahead of the f/x delivery date, at a time when the shop may still be in the midst of critical R&D. Temp effects and promotional shots eat up resources and time. And they're nitpicked by millions at a point when f/x pros might prefer not to be showing anything to anyone outside the office.

But they do grab fans' attention, as the "Iron Man" teaser did. So look for more stunning visuals in tentpole trailers to come.

Just don't count on them being in the film.