So, is rolling needed or not? Is it the default or not?
Rolling is not needed, it is an underlying model, and an historical context. Rolling (4d6) is the default to create PCs, with standard array and point-buy as alternatives. The commoner, the entry presumably most representative of the general population, is not consistent with any of those PC-creation methods, it is consistent with 3d6.
If you were to actually go to the trouble of generating the stats of every single NPC inhabitant of, say, a city then you'd get a realistic population with no stat limited by any other stat, some people being blessed with above average abilities across the board and other cursed with low abilities, reflecting that actual populations have this kind of variance.
Realistically, human abilities, when arbitrarily sorted into only 6 boxes like D&D does, aren't independent random variables. Some things, like strength & overall health are strongly influenced by the environment, and/or are linked to eachother. An athlete is likely to have higher scores in all three physical stats, in large part due to intentional training, for instance.
After all, it would be a ridiculously unrealistic world where every single person had exactly the same Str, Dex, Con, Int, Wis and Cha.
The degree of unrealism would be out there, but if that hypothetical single set of stats were very near the average, it might be less unrealistic than the comparatively tail-heavy 3d6 distribution. :shrug:
It would be just as absurd to have an entire population of tens of thousands of people whose ability scores added up to 27 points, implying that every person is equally blessed/cursed.
It would be a good deal less absurd, since at least they wouldn't all be identical.
Yet if you were to attempt to generate the same population as above, but using point-buy instead of rolling, you get that totally unrealistic population. Like The Stepford Wives gone global!
Similar to rolling 4d6 for the whole population, yes, you'd have a world that was, on average, well above average. 3d6 would work better, though it'd give you too much on the very high & low ends. But, you could have an 'mundane array' of 10,10,10,11,11,11 (which'd have the opposite problem, /no/ high or low end!), or a 15-point buy (the point cost of that very average array) with more variation depending on exactly how you used it.
You could get much closer to realistic (or what you considered realistic or even just desirable for the world you had in mind) by not using any PC-generation method (nor variation thereof) uniformly through the population, at all.
To the point of 'is 3d6 the default/is it required'? Yes, the default assumption is that the population is such that their abilities were randomly generated on 3d6 in order.
It's neither default, nor an assumption in 5e - it was way back in 1e, and it hasn't been changed or dismissed, it's merely been ignored since then. There's a whole morass of tribal knowledge, unquestioned traditions, and unstated assumptions underlying D&D, like a castle built on a swamp, the stone parapets are no indication of the foundation.
'If they haven't changed something, then it remains the same'
That's how it seems to me. The 1e DMG went further than any other D&D book before or since in spelling out all sorts of bizarre minutia, philosophies, and rationalizations for D&D, and most of that strangeness hasn't been explicitly 'changed,' just quietly ignored...
But seriously? We're arguing about whether or not a guideline last suggested decades ago, long before many (if not most) of the players of the game were born is relevant?
It's hard to fathom, but yes. Obviously, D&D is a game (and in particular, ENWorld a community) where the past is extremely relevant.
