This seems to be assuming a degree of player/PC identity which wouldn't make sense using the sort of approach I am talking about.That's the thing - not everyone wants to be driven by destiny. Some people want to steer their own course. Now if destiny beckons, they might follow, but they don't want to be railroaded into it.
To try and be clearer: the PC has a destiny (reflected by the +0.5/lvl); the player chooses her PC's path. The player is therefore not railroaded.
And I'm not saying that anyone has to play this way. I'm saying that the game can be played this way, and if it is played this way then the NPC guards having increasing levels as the PC's gain levels needn't be seen as leading to an inconsistent gameworld in which things get tougher as the PCs get tougher.
It's true that Rolemaster doesn't use many of these assumptions, though it's parrying rules and spell overcasting rules are (in my opinion) a clever use of simulationist-friendly rules to confer a degree of narrative control on players that is unusual for a simulationist-oriented game (it contrasts markedly with Runequest, for example).But from a simulation perspective - the NPCs don't become more powerful in the dramatic scene. They just have more luck this time.
If the .5 bonus per level (and the +6 hp per level) for some NPCs just stand in for the extra luck they have in the particular scene, the same could apply here, and I suppose that goes in the direction of pemertons point of view. (Though I wouldn't be surprised if pemerton just takes this point to facilitate an interesting discussion - considering he at least used to play a lot of Rolemaster which certainly doesn't use much of these assumptions.)
But I'm not merely trying to facilitate an interesting discussion - I'm trying to defend the legitimacy of a certain (non-simulationist, non-railroaded) approach to fantasy RPGing, and the utility of various mechanics for that sort of play.