Pokemon has continually become more and more front loaded as time has gone on:
Pokemon X and Y will do better than Pokemon Diamond and Pearl FW, that's for sure. Going as low as to say that it'll only match that? That's quite odd. Anything below 1.8 Million will be a surprise. Anything about 2.3 Million would be unbelievable, and won't happen.
That's very selective data to use considering that RS was a huge tumble from GS. Regardless, DP being higher than RS is not evidence of being frontloaded at all; although it wasn't quite in the same proportion, for LT sales, DP outsold RS considerably, too. The DS simply had a notably higher base to sell to, which allowed DP to perform better on the whole. Not gonna happen for XY.
As for BW, that's uncontestably an outlier. It was the first second generation on the same console and it had an enormous userbase to sell to. None of this applies to XY.
Also, we've seen certain major DS franchises decline considerably on the 3DS. Nintendogs, Brain Age, Layton, 2D Mario... While Pokemon is much more proven than these, it's quite possible it will lose the extra fans it got during the DS days and decline to perform closer to what RS did.
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