I found this little pearl of wisdom on OMG’s web page on MDA:
The MOF also defines a standard repository for meta-models and, therefore, models (since a meta-model is just a special case of a model).
They seem to believe that, if something applies to a subtype, then it automatically applies to its supertype too. That is Liskov’s substitution principle inverted!
And the OMG is supposed to be the leaders of the object world.