Lanefan
Victoria Rules
1e is glaringly, if quietly, inconsistent that way. "Men" (i.e. Humans), Elves, Dwarves etc. are all written up in the MM and given hit dice, meaning that by default they're supposed to use the monster combat matrix - but then they're also counted as NPCs, with 1.5 sets of different mechanics depending whether they're levelled or not; or as PCs/henches/hirelings with different mechanics again, some but not all of which overlap those for levelled NPCs.(1) Where is this assumption built-in? Not into AD&D, which uses different to-hit tables for a half-orc depending on whether the half-orc is a PC or NPC (see Gygax's DMG p 74).
Tossed all that ages ago. As best I can manage it, an Elf is an Elf is an Elf whether PC or NPC or opponent. Any of these might be levelled (and PCs always are, barring any recent unfortunate encounters with level-drainers) or might not be; in any case they all use the same mechanics.
4e had some good design ideas. This was not one. In fact, in an edition that also had considerably more than its share of bad design ideas this one was, if not the worst, mighty close to it.Not into 4e, which uses different character build principles player-side and GM-side.
3e was squarely on the right track in having everyone - PC, NPC, whoever - use the same mechanics, but it then blew it by having far too many mechanics that everyone had to use.

Semantics. Narrating relatively static or inactive things (terrain, buildings, weather most of the time, inactive or peaceful creatures or people, etc.) establishes the scene. Narrating anything involving an NPC doing anything significant - and a fight between two NPCs leading to the death of one certainly qualifies as significant - is simply (and quite reasonably) short-cutting out all the action resolution that'd be involved if it were a PC doing the same thing.(2) The GM narrating the results is not "cutting to the chase". It's not a mode of action resolution. It's framing and/or establishing backstory.
It's assumed all the action resolution took place the same as if PCs were involved, but for the sake of sanity those actions don't all get individually played out; all that happens is the GM narrates the results.
An example: when the GM narrates "Over breakfast the rumours are confirmed: the chambermaid woke up dead in her bed this morning, her throat slit by an assassin during the night." what's being left out of that narration is all the climbing and lock-picking and stealth and to-hit/damage rolls from the assassin along with any rolls the victim might have got in order to awaken and cry for help, yet it's assumed those all took place as they would have done had one or both of those involved been PCs. Here, to save tme and get on with things, the GM just narrates the result.