A NP is representative of the Hero's legend- Gil has GoB because Legend says that he owned everything. Cu has Gae Bolg because he never missed the heart. Saber has Excalibeams because she killed 1000 men in one slash. etc, etc
CG are heroes without legends. No Legend=No NP.
Archer is just a cheating cheater who happens to have a hax ability that grants him a pseudo-NP.