Geographical location has no bearing on a genre
You forget that Genres are often agreed upon definitions that sometimes are ENTIRELY unrelated to the content of the game.
JRPG and Western RPG are one of those. They refer to their country of origin irregardless of game and content.
A similar Genre of game? Independent
Independent games can be ANYTHING, their status as a independent game is based purely on the producer and developer.
Independent isn't a genre, its a production and financing means. It is not a game play aesthetics. And you are right, it can be any genre, because it has no bearing on its genre.
Besides there could never be an agreed upon definition of JRPG because... what is a Japanese RPG if it isn't a game from Japan? Legend of Mana is just as important as Final Fantasy... Tales of Symphonia is just as important as Tactics Ogre/Ogre Battle
As far as Western RPGs go I'd almost challenge you to think of some classics outside the dungeons and dragons copies. The diversity of Western RPGs is just as grand from Ultima to albion to fallout to Elder scrolls.
The core play aesthetics are two things for jrpgs.
When you're trying to figure out the core play aesthetics there are two questions you can ask:
Is
BLANK an element of the game?
And more importantly, you ask: Is
BLANK the reason why I play the game?
Fables matches the core play aesthetics to that of a jrpg then any other genre
Actually it is pretty western. The Morality system, the way it tells its story, the aestetics (check how Japan does Europe and see)... The way the game flows and how the game handles its characters (especially the female ones... ESPECIALLY ITS FEMALE ONES!)
How it tells it story, isn't why you play the game, its the games influences. The morality system isn't why you play fable. (and You in this case isn you personally, but a broad more general you).
The core play aesthetics for a jrpg : Narrative (being the primary reason why you play it). You (this you is personal), aren't the main character, but you the player, are more like a director and voyeur keeping in on their lives and directing their actions. Whereas with a Western RPG, the main character is you, and decide the story, and its order. While Narrative can be a strong reason to play a western RPG, its not its Core, its foremost core game aesthetics. Western RPG core play aesthetics is escapism and expression. Its about immersion of the player into the role and world and letting them define who they are in said world, going as silly as adjusting brow height. But its more to that, such as character class selection, or making your gear set to conform to your play style. That too is a form of expression. And while these elements can be found in JRPG, again, I must stress, they are not why you play JRPGs.
Much in the same way, we ID Fallout as a western RPG, but not a FPS even though you spend a great amount of time in first person, shooting things. Or why Black Ops is a first person shooter, but not a RPG, even though it has a leveling system in multiplayer.
To put it more simply JRPG tell you a story, where as a western RPG place you in a story. While similar, but they arent fairly different way to convey a game to the player, and their fairly different reason why to play the game.
Fable has expression as a high level game play aesthetics but its main one is narrative. It tells you a story vs. placing you in one.