Unless it's military grade. Accidental GreyGoo can't use StochasticEvolution? to evolve means for transporting itself, coordinating its actions, penetrating hardened substances, or doing anything intentional. It might be nasty stuff to have circulating in your bloodstream or water supply - but no nastier than any natural pathogen or invasive weed. It's not smart enough to spontaneously solve any of the obvious NanotechDesignProblems.
For some reason, the absurd energy requirements for a GreyGoo nightmarish scenario are hardly ever mentioned, but that's the number one reason why it won't happen.
The cells of biological organisms contain elaborate mechanisms to ensure that DNA copying is accurate.
Thats not the point of AboutCells. Structurally can mean many things, it just provides a unit of (inter)processing. Of course cells are the unit of DNA copying.