With the plethora of gaming supplements -- books, pdfs, magazine articles, etc. -- available to add variety and personalize your campaign, it's nearly impossible to justify why an NPC can't do something during a game scene. New spells, feats, prestige class abilities, templates, variant core classes ... the sky's the limit when you need to design an encounter.
Combine that with the DM's legitimate right to roll his dice behind a private curtain, and I have to wonder why anyone would bother keeping track of elaborate NCP character sheets... Merely maintain the thrill of adventure regardless of how much "fudging" it takes...
So be honest. Do you actually keep track of all the esoteric digits? Isn't it OK for the ends to justify your means?