The SI units absolutely include newtons and millinewtons. The derived units (http://physics.nist.gov/cuu/Units/units.html) and prefixes (http://physics.nist.gov/cuu/Units/prefixes.html) are both part of the SI.

Also, remember, people are representing these numbers on computers. Derived units are very useful—in fact they are often critical to achieving necessary accuracies using compact representations. Further, representing quantities in terms of other unique, problem-specific units is often extremely helpful for ensuring good numerical behavior.