once again some people aren't thinking this out, first of all the amount of stuff we can carry is a representation of the amount accesible to you, so for instance in fallout 3 you weren't really able to carry 250 or 300 lbs of stuff, nobody can carry 8 weapons like i did and tons of other supplies, its a representation of whats easily accesible for you to get in the same way lets say the town of megaton doesn't really only have 20 people in it, each person represents x number of people, so megaton prob would of really had a couple hundred people more or less not 20, or rivet city, it would of had way more than 25 people, aircraft carriers can hold thousands of people or at least hundreds. so its not different with carry weight, if you're looking at it like you're actually lugging around 300 lbs like you could in FO3, its not what you can actually carry all at once, its a REPRESENTATION.
Fallout (the original) dealt in the abstract (both in combat and in locations); but Fallout 3 went out of it's way to "Show and not tell", and to put the player in the PC's place.
Stats [in FO1] depict the archetypes. A strength of 5 means that your PC is of average strength ~a 10 means your PC can hold their own with professional power lifters.
A person can usually carry a more than they can lift... (if its well packed)
The inventory was not abstract as far as I can tell. None of the games accurately depicted a back pack (but at least Fallout 1
had back packs!)
Weight was a factor; I don't think weight would be a factor in an abstract (accessibility based) inventory.
As for stackable inhabitants... I know exactly what you mean (and Vault 13 had it), but I'm not sure they meant that as literal in FO3. Vault 101 had inaccessible areas with (real and implied) inaccessible NPC's. You see it done in RPG's (like FO1), but in FO3 (and Oblivion) it would seem to go against base principles.
(and I'm near positive they did not mean it that way with the inventory)