I have always run that anything the PC's use, the NPC's can use... and vice versa.
That does not mean that the NPC's cannot introduce a new Feat or ability to the game... every once in a while I find a new Feat that fits well, such as Spear Fighting.. surprising the living daylights out of my players and created a 'thats cool' moment.
Given the opportunity, those players could seek out that training and take the same Feat.
One comment I would like to add to the mix, I have had good experiences relying on my players to understand how thier characters abilities work. I don't need to know the nit-picky details.
What I do need to know, before it happens in my game, is how certain synergies can spin out of control. For that, I come here and ghost along the Rules forums. When I see something that will impact my game, such as the recent Entangle thread.. I see how other GM's are handling it and find a fair path to present to my players before it comes an issue.
The only time I have had a problem is one player whose comprehension level creates some confusion when he reads the rulebooks. Unfortunatly he also has some liguidatable cash and tends to buy said rulebooks

My other players don't even own the PHB. All my players concede to the flow of the game and I refuse to have indepth rules discussions mid combat.
I agree with a poster upthread who mentioned that DM fiat is sometimes the transparent effect of an unknown quality that the PC's face. An example from a recent game.. I had a Fey strike from within a waterfall at a monk who chased said Fey. The Fey got Sneak Attack damage depsite not flanking nor being completely invisible. Player got upset as it went against the rules as he knew them and could not grasp that *this* Fey had a special attack ability that allowed the action as an exception to how the rules usually worked.
{to put a bit of perspective on this.. said player complained about being 'taken out of the fight' as he was 'severely wounded'.. at half HPs, still more than the Mage who was engaging in melee combat with a dagger...the character retreated from combat and sucked down potions of healing for the rest of the combat.}
I think the whole power thing comes down to a matter of presentation.
Players have more power to affect how the game plays out, as thier choices must have impact on the style of the game for them to gain full benefit from thier choice {see 'Arrghh.. my rogue sucks!' thread...and others of its ilk}
DM's have more power by being able to shape these choices.. and thereby the style.. by allowing/veto's of material.
Roleplayers of all stripes have more power to provide thier own fluff on top of a relativley stable base of crunch..without recreating the days of 2e where you never wanted to join a new group because of the effort it took to learn all the new house rules.
In previous version, house rules were required to set the style of play. In 3X, fluff can set the style while still using the same D20 mechanics. The previous 'jump over a 4 foot wall' is a testament to that. 3 posters used the same basic mechanics.. yet described the action in 3 differing ways.
There are still loopholes and areas that are not addressed fully.. the reason I ghost at the House Rules forum as well! Much of the 'I need a HR to cover that' ends up being.. 'I will use mechanic X, as it is close to what I need but will call it Leaping Tumble over Wall check instead of a Jump check.'
Anyway.. I am starting to ramble.. and its only been 15 hours on the job. Time for me to go home
