Sure, but they can't.
That ties their hands when they release future rules and supplements. If halflings are assumed to be one thing, then nothing can come out that severely contradicts what the core rules assume they are, and nothing can come out that tries to exclude them, because "people will expect them." Suddenly, the Nordic or Aurthurian or Gothic Horror setting needs to somehow find a role for Bilbo Baggins or whatever, even if that contradicts the tone of the setting.
That's a bad predicament.
Those who want a default setting can buy a setting book. Or an adventure with a town in it. Or whatever. There's no need for a core setting. There's a million different ways to help out newbie or time-sensitive DMs. Jamming an expected world into a supposedly modular core rules base isn't a great way to solve the problem, since it hard-codes the setting assumptions into the base rules, making them difficult to remove.
If you didn't want eladrin or dragonborn or tieflings or tricksy halflings as a core race in 4e, you were SOL, because there they were, in places where maybe they didn't need to be (FR or Dark Sun, forex). To avoid that problem in the future, the game needs to be setting agnostic at its base level.
Want to have a setting done for you? Buy a setting book. That's what they're there for.
I just have 2 questions.
1. What part of telling players "I dont care if dragonborn are in the core book. I think they are stupid and they dont exist in this world, pick something else..... was difficult exactly?
I've been doing it for years now with no problems.
and 2. What if i dont want to have to shell out another 40$ for an entire setting book just to have a little framework?
I find some of the statements here hilariously contradictory.
I.E.
" if theres a class with fluff in the rulebook, like for instance the knight of corinthian (Which for example is a fighterish class with bonuses to riding because Corinthian is famous for horsemanship and perhaps is even a mongol style civilization) then its just waaaayyy waaaayyyy waaaayyyy too hard for me to find a town like that somewhere in the entirety of my homebrew world. so that just cant be in the rules.
"The concept that I, me, must find a single city with a horse warrior culture somewhere in the entirety of my planet simply boggles my creative ability, handcuffs me in ways that break my enjoyment of the game and most importantly is far too much work to integrate"
Immediately followed by
"I must be free to develop the entire world like i want without having any assumptions whatsoever thrust upon me." Nevermind that the 2nd is absolutely impossible unless you remove all racial abilities and adjustments to scores and just made everyone humans in funny clothes. Whats most funny is the inherent silliness in the argument.
I remember there was a something of pelos in the 3rd addition. PrC for religious characters i think but its been a long time. I remember they squashed undead really good which was the real point.
Anyway i remember there was a good bit of fluff with it. But my world had no god pelos. Oh noooossssee what do i do?
I said the player who wanted it could have it but it was the something or other Sol. Our god of the sun. whew, problem solved.
I also outlawed ninjas. Which if anyone remembers those class books WERE considered core at the end of 3e so was the same as outlawing something in players handbook.
Didnt break my game to take out a specialty asian/western version of asian thieves. We had an asian part of the world. They had rogues. Rogues who spied on people and carried out assinations were called ninjas and belonged to clans.
Players who wanted to be a ninja could take it or leave it. No one really cared.
Its the easiest thing in the world to ignore fluff you dont like. Including it doesnt hurt anyone.