I don't think I did miss the point.
Judging from your description of your game, social interaction makes up a big part of it. It's also quite clear that you expect players to make a fair show of acting "in character"--which usually means that there will be situations where the player's understanding of the right choice of action and the character's understanding of the right course of action differ. And in that situation, the player is expected to follow the character's lead.
It's quite possible in your game that NPCs don't often get exact scores for their active social skills. Maybe you look at Baron Nogoodnik's character sheet and it says: "Diplomacy good, bluff moderate." I presume it still has to say "Sense Motive +10" because "sense motive:good" doesn't tell you whether the PC's bluff roll of 25 succeeds or fails and nothing short of "sense motive: yes, every time" would enable you to determine whether he, as a reasonably insightful NPC can see through a player's good but not prefect lie. (I presume players still roll bluff checks for that sort of thing). However, that still has several inherent problems:
1. When Sense Motive is an active skill, the players may still ask for rolls. In that case, you'll need an exact bluff score if you're using it at all. With your method, if you don't roll the bluff at all before the sense motive is called for, it's not clear how you know whether to play Baron Nogoodnik's +5 bluff as a 6, 15, or 25--and it seems fairly clear to me that you usually DO play the interaction before the dice are rolled. Otherwise the "my name is/ Sense motive of 35, is he lying?" difficulty wouldn't seem so alien to your game. So, at some point, the mechanics will need to be in place. And with your method, the mechanics may not match what you played. If instead of Baron Nogoodnik, it's Councillor Liar with a +15 bluff making the check, you'll probably play him like it's a really good bluff--because he usually makes really good bluffs. But, if you roll a "1" on his bluff check when a PC calls for sense motive, the bluff you played as very effective is revealed to be pretty weak by the check.
Active sense motive doesn't remove the necessity for NPC bluff skills (though it may for diplomacy rolls). It just introduces a level of potential inconsistency between what the players see (which may be a very convincing bluff) and what their characters see (which may be a unusually bad lie from councillor liar).
2. It creates unnecessary character/player knowledge dichotomies. I consider myself reasonably insightful. I can often pick up when a story is inconsistent. On occasion, I enjoy playing a slack-jawed or smart but foolish barbarian. So, in your game, when my reasonable insight+knowledge of how you run the game (these are not really seperable items) indicates that an NPC is lying, I'm left with the question of whether my character knows what I know. Now, I could presume that my character is an idiot and doesn't know anything but it's always struck me as poor role-playing to assume that a character who isn't smart always does the worst possible thing. ("My character wouldn't know to try fire on these regenerating trolls" well, when he's grasping at straws to hurt something that isn't hurt by steel, why WOULDN'T he try fire. It's one of the obvious things to try). In order to resolve it, I could go on the basis of a sense motive roll but it will be tedious to try that on every possible lie I detect. (If sense motive is passive, there is a sharper distinction between player and character insight which makes this decision easier).
3. Sense Motive involves a lot of things that aren't actually discernable on a DM sitting down behind a table. For instance, in a PBEM, I once played a paladin who joined a troop of evil soldiers in order to determine whether or not they were responsible for an atrocity we had sworn to avenge. As I verbally duelled with their leader, I noticed that the bannerman kept fidgeting and shifting his grip. My thought: he's obviously quite new to the job if he hasn't figured out how best to hold the banner yet... or he's someone who isn't the normal banner man in disguise. As the game wore on, I discovered that I was right and he was actually a powerful wizard in disguise.
Sense motive acts on details like that. As a DM, you can include them in a verbal description and let the players figure them out. This however, has a couple of negative effects. First, describing these inconsistencies calls the players' attention to them in a way the characters' attention might not be. It assumes the PC made the sense motive, etc. Second, describing details makes the game take a lot longer since you'll have to put details in all encounters so that details don't become a de-facto indication of deception. Now some description for most encounters is good but with anything reasonably subtle, you don't want the inconsistency to be one of the three descriptive factors/NPC I've heard recommended for good DMing. So it necessitates going overboard or cheating the players out of clues their character should get.
4. An NPC may be like Schroedinger's cat and it may never be important to know if he's got a +12 diplomacy score or a +14. However, the difference between a +12 and a +14 bluff score WILL be important (as discussed above in consistency). Furthermore, even the schroedinger's cat like NPC will have good, better, or best diplomacy. There should be a difference between the guy with a +20 score, the guy with a +25 score, a +30, and a +35. (All of which are achievable by mid-levels--not that PCs don't interact with high-level NPCs from day 1).
5. Both PCs and NPCs are still constrained by the limit of the player and DMs' acting abilities.
I understand that some people shouldn't play some characters. I'm also pained when a stutterer tries to play James Bond or Captain Blood. However, I don't think one needs to be Sean Connery, Pierce Brosnan, or Errol Flynn (and have a crew of writers giving you a script) to play those characters either. This means that, assuming that you and your players are reasonably skilled actors, etc, the best your game will be able to approximate is reasonable skill. If you want, William Jennings Brian, Hannibal Lector, Johnathan Edwards, Savanarolla, Loki, Daniel Ocean, etc in your game, you're going to have to let the dice do a fair amount of the work.
6. I still think your system falls prey to what others have been referring to as the "he went that way" syndrome. Presumably either everyone asks for a sense motive check in that situation or you try to act it out. However, acting like a mediocre liar who half the party MIGHT detect in a lie is a very challenging task and I doubt that anyone is up to that kind of thing on a moment's notice. Generally, it will either be too obvious or too good.
S'mon said:
ElderBasilisk - nice rant, I'm impressed!
I think you're missing the point. For us the rules, including NPC stats, are there to support the GM's running of the game, not vice versa. No NPC 'has' a +30 Diplomacy score unless we actually give them a +30 to a Diplomacy role when it's rolled in play. Rules are primaily for players, for their PCs, to help them interact with the environment, and for the GM when they need a rules calling on something - combat, especially, can benefit from complex rules. So a PC can have '+25 Diplomacy' - that means they'll always roll +25 on d20 Diplomacy checks; but NPCs are more like Schrodinger's cats, you can't nail them down until & unless their stats are actually used - of course we normally detail combat stats, at least, and we aim to be consistent in our rulings. For us the rules are not a Platonic Ideal that defines the universe, merely an aid to running a good RPG.
