They invite you to change all the rules, which includes the height of dwarves as much as it includes what you add to something you're proficient in
The height of dwarves has never been a rule, though, in the sense in which RPGs present themselves as containing rules. No D&D book has ever presented it as such; and even when I first read Moldvay Basic it was obvious that stuff like the colour of a halfling's hair is not a rule in the same way as the stat requirements for playing a halfling.
The ways in which this is so are myriad, but here's one salient one: the rules for stat requirements for races in Moldvay Basic and AD&D are clearly meant to play some sort of balancing function as well as ensuring that races hue to archetypes; the descriptions of hair and skin colour are flavour.
There are outer boundaries somewhere - halflings and dwarves, inherently in their names and in the former's STR limits in AD&D, are clearly shorter than humans. Elves, given their CON penalty in AD&D, must be slighter than humans. But if some AD&D-er or Moldvay Basic player decided to follow JRRT and have elves be as tall as or taller than humans, that would not be a change in the same category as changing the stat requirements for playing an elf.
Well, for one, remember that a list of Corymrean noble houses that you can plug into your character's own history *is* a rule. So if that's all we got, that might be enough support.
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I don't think that separating lore from rules achieves this goal. In fact, I think separating lore from rules undermines that goal. It creates a second class of game mechanics (the lore) that "doesn't matter" and so can be changed and trod on and disregarded and trivialized, while the "more important" rules (roll 1d20 to hit; six ability scores; fighters are a class) become unreasonably entrenched and unable to be changed.
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If your backstory isn't informing the motivation and role-playing of the character's current behavior, then it's as superfluous as the appearance of a queen in chess.
I find all this pretty hard to follow.
First, lists of noble houses aren't "rules" in the typical way that word is used to describe RPGing. It's a piece of setting information. Someone who changes the list isn't chaning a "rule" in the way that would be the case to grant Cormyrean nobles a +1 to hit with mounted lance attacks.
But the idea that such a list somehow improves the play experience, or fills an otherwise problematic gap, is also something I find weird. The original Oriental Adventures book has no list of noble houses to follow. It has rules (relatively confusing, perhaps even contradictory ones) for determining a character's family background and some elements of that family's members and history. But the group also has to make stuff up (eg if the Ancestry table tells you that one of your ancestors was a great general, you have to make up the details of that).
Oriental Adventures wouldn't be
better if it just had a list of noble houses. It would be worse. It's system for generating families, despite its flaws, is fun and produces interesting results that generate immediate play buy-in. It's a much more engaging way to generate backstory, in my experience, than looking down a list of noble houses that reflect someone else's play experience and authorial ambitions.
Part of how you communicate better about expectations is by making those expectations less flexible, so that they can be safe assumptions.
Who does the "you" here refer to?
Presumably not WoTC: they want the expectations of customers to be as flexible as possible, so as to foster sales.
And not me - why do I want my players to have narrow expectations? Maybe I want to try different things with different games (eg I'm hoping my 4e Dark Sun game will play differently from my 4e default cosmology game).
At this point you seem to be going beyond the Burkean conservatism that [MENTION=6799753]lowkey13[/MENTION] has been engaging with to a claim that any deviation from a pre-given script is a threat to the stability of game play. Your conception of RPGing, as it is coming across in these threads, seems to take aim at just about everything that I think is worthwhile about the activity!