Umm not my understanding of what has actually happened. Like most sports from time to time the teams make certain claims about performance. To nascars credit and unlike Avesco who are under the control of HRT, they judge these claims on merit.
For the year 2002, Nascar introduced new areo measures. It was found that these measures impacted adversly on the Fords. Wind tunnel testing in fact confirmed the the Fords are producing more down force and in the interest of not giving the fords any more of an advantage on the short oval approved the changes to the lips. Now this also has the effect of improving the Fords and for that matter the dodges performance on the super speedways.
Now Gm retric would have you believe that they have the best engineers the best of products and that there should never be a parity adjustment. Ford should be able to get it right!. Part of it has merrit. Part of it is absolute BS. When you have too much down force there is only so much the rules allow for. Nascar should be praised for finally reacting to a serious balance issue to the parity.