pawsplay
Hero
It also occurs to me that - in my parlance, at least - the term NPC has actually changed its meaning over time.
Whereas NPC has now come to mean (in my mind) any character not controlled by a player, it seems that the term used to be used more explicitly with reference to those characters with PC-class levels:
i.e.
the 3rd level Dwarf fighter is an NPC
Bob the barman is a Normal Man, or "scenery", or an element in the game - but not an NPC in any significant sense.
Does anyone else perceive this shift of emphasis in meaning, or is it just me? I am not suggesting a hard divide here; simply more of an emphasis.
That is correct. Although other games treated the term differently, 3e was the first edition of D&D to consistently refer to all non-PCs as NPCs; previous editions generally referred to a 2 HD Veteran or a 1d4 hit point Normal Man as a "monster," although this had no significance except as to how you detailed their characteristics (for instance, no abilities other than Intelligence, and great strength only by inference from having a bonus to hit or damage).
It's also worth noting that a 1 HD monster has all the capabilities of a 1st level fighter in OD&D. In a few cases "monsters" are noted as actually being Fighters. Taken together with the notion that, in addition to these Veterans and Brigands running around, there were explictly knights who were 1st level fighters, it should be clear that NPCs with class levels are not unusual, Fighters even less so than most. Anyone who can pick pockets absolutely must be a Thief in AD&D, or some special "monster" with thief abilities. In the absence of particularly distinguishing characteristics, a 1st level fighter is a competent, but generally rather ordinary being. If he makes it to 2nd level he becomes exceptional. It's not until 3rd level he really qualifies as particularly heroic.
What makes wizards different, in AD&D, is that, basically, teachers or books are hard to find, and a certain slice of the population lacks the Intelligence to reliably learn any spells. 3e carries this idea forward, with spellcasting ability depending on a Ability Score such as a wizard's Intelligence. Being a 1st level wizard isn't more of an accomplishment than getting a Bachelor's degree, or self-teaching a trade. In the Dying Earth, learning a simple spell required only literacy, although the unc-clever were likely to die of overly ambitious efforts.