Originally posted by the ninjak
That is because the film Ironman armor tech has next to no actual defensive technology.Tony in the films just has highly durable armor. In the comics he has electromagnetic fields and most importantly Inertial Dampeners.
Which greatly increase his defensive capabilities.
The film version of Ironman is greatly lacking in the tech department. Which is a shame because the writers thought the public couldn't handle it.
Even the recent animated series Avengers: EMH gave Tony such powers. And not surprisingly they cancelled the series and replaced it with a more film friendly version, Avengers Assemble. Which sucks.
A great example of films influencing comic canon in a negative way.
I think the public couldn't swallow Tony creating force fields for the armour; advanced as the armour is, that would be too far out for them to buy.
Now, if he gets some alien tech somewhere in a future Avengers film and incorporates it into the armour, creating shields, that would be believed. We saw lots of force shields being used on Asgard in the new Thor movie, and people accept it without question because it's an otherworldly/alien realm with advanced magical tech we don't understand. In Avengers, the device creating the portal manages to shield itself because the power source is the otherworldly Tesseract.
I think the writers made the right call for now. And there is precedent in the comics of Tony getting some alien tech into the armour; his armour in The Heroic Age gets scanned by Ultron, who observes it now contains some Kree tech.