The 10th Amendment reserves powers to the states and to the people, respectively, not to the United States, which as a corporate entity, is bound by the Amendment.
I've been following this discussion and thought to add a note of fact to the proceedings. I suspect I will just get flamed.
The 10th clearly acknowledges powers delegated to the United States and that the states and the people retain rights not delegated. It offers no Constitutional justification to usurp powers delegated by the Constitution to the United States.