Emerald was released before the DS in its Japan, but due to localisation times, it just so happened to release in America after the DS came out. And Black/White released in the Americas around the time the the 3DS was out (while in Japan, it, again, released before the 3DS was out). Granted, the difference here is that this is a new generation.
However, Black 2 and White 2 released in Japan during the 3DS's second year of sales.
To point out your little strawman argument: to say that it wouldn't take advantage of the 3DS in its current state, of course you'd be correct - there'd be no benefit. If they had planned to release the games for the 3DS, they would've at least taken more development time so that they could actually get the game on it and looking spiffy enough for release.
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