It's already confirmed that B/W will be able to communicate with Gen IV in some way. The Movie 13 Legendary Beasts are supposed to unlock somethin' in B/W. I'm glad honestly because we've been able to transfer Pokemon over to the new generation since Gen III. I don't want all the Pokemon I've raised to be trapped in Gen IV forever.
I do think B/W should have fewer old Pokemon than previous generations, only the basics (Geodude, Magikrap, some Bugs). I don't see why people would want them to cut us off from Gen IV, it's counterproductive.
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