Dynos aren't foolproof, and can easily be made to lie by changing the temperature correction factor.
Even 2 runs, 10 minutes apart can show wildly different figures, and if the temp in the workshop where the dyno is can vary, such as opening a door to let a cool breeze in, you can also get more power.
Personally I don't believe it, and never will, unless I can witness it with my own eyes, and look at the settings for each run. Just as Jase_ELXR8 has said, the manufacturers would soon be onto it, as anything that helps emissions and economy whilst increasing power has got to be a positive marketing point.
If it did work, I think Saddam Hussein would send his henchmen in to destroy the company. He wouldn't want to lose a few extra dollars of crude now would he?
My cars not on fire, that's just the tyres.