There's something that's being missed with the broad brush strokes here.
Just because something can be put into the setting doesn't mean it has to. And, just because it's there, doesn't mean it's common place.
I don't think WotC is going to start referencing other books in the creation of their campaign setting. They're not going to say "This NPC is an Avenger. This here is a group of Avengers. Avengers work for this government. This is a tribe of Avengers." (The sidebars in Player's Guide to Eberron are a horrible culprit here). At the same time, they aren't going to say, "Class/Race X Y and Z do not fit here, do not play them, they are not allowed."
Even if the class or race doesn't fit if you injected 1,000 or more into the campaign, it's still possible to drop it in without disrupting the setting. Being "The first/the only/the last X" can go a long way.
Additionally, with some twisting you can tuck seemingly unreasonable stuff into the Setting proper. This was done quite a bit on Eberron's messageboards; someone would want to play Oriental Adventures-style Samurai/Ninja, but there's no "Asian" cultures that support that. However, it's easy to say "This clan of Samurai fits with this nation's Noble warriors. This clan of Samurai fits in with dwarves. Ninja fit with the practices of This or That group, because they're all about skulking in the shadows."
I really don't get the impression that, because Splatbooks exist and it's considered "Okay" to use them, that this will come in and ruin the setting. I'd really like KM or Wik to give an example to illustrate their point. Because right now, I can't help but think it's the equivalent of "In Dark Sun, metal is rare, but the PHB says that weapons are metal. Using the PHB ruins Dark Sun!"
Wizards have always existed in Core D&D, and yet Dark Sun could come in and say "Magic? That's messed up. It messes up the world. Magic is bad, m'kay?" And that didn't cause a fuss. So, where's the fire?
Just because something can be put into the setting doesn't mean it has to. And, just because it's there, doesn't mean it's common place.
I don't think WotC is going to start referencing other books in the creation of their campaign setting. They're not going to say "This NPC is an Avenger. This here is a group of Avengers. Avengers work for this government. This is a tribe of Avengers." (The sidebars in Player's Guide to Eberron are a horrible culprit here). At the same time, they aren't going to say, "Class/Race X Y and Z do not fit here, do not play them, they are not allowed."
Even if the class or race doesn't fit if you injected 1,000 or more into the campaign, it's still possible to drop it in without disrupting the setting. Being "The first/the only/the last X" can go a long way.
Additionally, with some twisting you can tuck seemingly unreasonable stuff into the Setting proper. This was done quite a bit on Eberron's messageboards; someone would want to play Oriental Adventures-style Samurai/Ninja, but there's no "Asian" cultures that support that. However, it's easy to say "This clan of Samurai fits with this nation's Noble warriors. This clan of Samurai fits in with dwarves. Ninja fit with the practices of This or That group, because they're all about skulking in the shadows."
I really don't get the impression that, because Splatbooks exist and it's considered "Okay" to use them, that this will come in and ruin the setting. I'd really like KM or Wik to give an example to illustrate their point. Because right now, I can't help but think it's the equivalent of "In Dark Sun, metal is rare, but the PHB says that weapons are metal. Using the PHB ruins Dark Sun!"
Wizards have always existed in Core D&D, and yet Dark Sun could come in and say "Magic? That's messed up. It messes up the world. Magic is bad, m'kay?" And that didn't cause a fuss. So, where's the fire?
