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Regardless, version-locking characters is retarded because, unlike Pokemon, characters have a bit more meaning to them and players might wish to meet all of them in their games.
It's simply compensating for the fact that Pokemon has no real RPG mechanics, so your "choice" is limited to the version you buy. Version-limited storylines sound cool on paper and hasn't been very glaring yet (mostly due to how weak the storylines are anyway), but they might at some point.