Maybe Stark can come up with something to make his armor resistant to magnets. Because science IS MAGIC.
Also, it's Captain Obvious territory at this point - wasn't the point of that teaser to show that the fight is interesting because one's weapon/armor is the one thing that his enemy has complete control over? (the fact that the armor is coming apart and we see tony's disgusting manhair seems to show that the writers didn't forget about the iron/metal/magnets thing. It's more likely the character didn't think, and he was written that way).