It's nonsensical to think that if you have even a single stat that falls outside of the range given in those arrays, you are somehow kept from ever being a PC. 65 magical PC stat ranges and the rest you the world is left out in the cold.
He's probably imaging a world where there isn't Inspector 12 measuring all of the people who want to be PC adventurers.
Inspector 12: "Sorry Bork, you have a 17 strength before racial bonuses. I have to stamp you an NPC. Next!"
There are doubtless multiple individuals with that combination of scores. However, it strains credulity that so many of them turn to adventuring as a profession where those individuals within the population who happen to have a 17 strength and a 7 dex (or the reverse) do not.
The inconsistency is that the PCs are thus drawn from (one assumes) a subset of the population rather than the entire population. The bell curve tells me there's going to be members of the population out there with Intelligence 18 and Wisdom 7 - why can't I play one of those - or at least have the chance to, should the dice be so kind?
Being a PC or a NPC is not a property of a character in the gameworld, so all of the above is pretty strange. (And really, [MENTION=6787503]Hriston[/MENTION] made this point upthread already. EDIT - including in a ninja post just above this one!)
Not to mention: if there is an NPC in play, and a player wants to take it over as a PC for whatever reason, presumably no rule prevents that if everyone at the table is amenable. (They may not be amenable if the stats are completely broken, but this would be a time for ad hoc rulings rather then applying the default PC-generation rules.)
And as [MENTION=22779]Hussar[/MENTION] points out, no PC can start the game as a wealthy person, or a poor person, or a king, or a shop-owner or farm-owner, etc; yet presumably the gameworld contains plenty of such people who are in-principle amenable to an adventuring life.
The rule that PCs must be built within certain mechanical parameters for stats is no different from the same rule vis-a-vis wealth, or race (why can't I play an adventuring hill giant?), or inherited magic items (why can't I play an adventurer whose grandma bequeathed me a vorpal sword?). It's a rule intended to achieve balance across participants in the game.
If the PCs are in fact your game world's only classed-and-levelled people then their generation method becomes moot - they just are what they are. But if they're not, and-or if your answer to question 2 is 'yes', then the distribution of stats among all the various level-gainers (including the PCs, who are obviously part of that level-gaining population) should reasonably mirror that of the population as a whole
Why?
I've never played a D&D game where (i) the GM has rolled up every inhabitant of the gameworld, then (ii) the players dice to see which one of those inhabitants they get to play.
But if I did, I can easily imagine the GM saying "Well, these ones are off-limts" (the kings, the merchant princes, the inheritors of vorpal swords, the super-strong heal giants and super-magical liches); "These ones aren't really viable" (the maimed, the very old, the very young, the dirt poor, etc); and so on - until we get a list of eligible characters for play who could be constructed using point buy.
Point buy just cuts out the needless busy-work for the GM!
(By the way, there is an excellent fantasy RPG in which a starting PC can be a prince of the royal blood; or a merchant prince; or maimed; or dirt poor (it also has rules that would support a king or a lich as a PC, though to actually start with such a character would require a deliberate departure from the default PC-build rules). That game is Burning Wheel; but it adopts a very different approach to "balance" across player characters from the D&D approach.)