I think it's just a case of people getting carried away. It's certainly possible to make your car fly... I've got a replay downstairs of an NSX in GT1 getting about twenty or thirty feet up off that last turn in Trial Mountain.. it went through the bridge.
I think what's happening is that no one knows how to properly use Photo Mode yet. So they're going for the "wildest" pictures rather than the best pictures.
Also bear in mind the lack of damage. A Zonda could probably get that kind of air in real life.. the problem is, it wouldn't be in one piece when it did it. Neither would the driver.