3rd week sales from Famitsu:
1996-03-11 [NGB] Pokémon Red / Green - 5,756 / 136,216
1999-11-29 [NGB] Pokémon Gold / Silver - 453,500 / 2,317,549
2002-12-02 [GBA] Pokémon Ruby / Sapphire - 321,408 / 2,037,949
2006-10-09 [NDS] Pokémon Diamond / Pearl - 291,178 / 2,311,331
2010-09-27 [NDS] Pokémon Black / White - 372,619 / 3,782,076
- Red /Green was probably sold-out that week. Weekly sales are: 109,207 -> 21,253 -> 5,756 -> 22,053 -> 28,551. Clearly an odd low. Also, overall numbers might have been adjusted by Famitsu.
- Gold / Silver numbers might also have been adjusted by Famitsu.
- Ruby / Sapphire was launched when GBA LTD was 6.5m. While I think people like to throw the installed base excuse too lightly, I think it was a factor for the initially slower sales, along with stock (see blow).
- Diamond / Pearl, DS LTD was 11.3m, but the game sold-out at launch. I don't know what the stock situation was in the following weeks.
- Black / White. Plenty of stock and DSes around.
The truth is up until B2W2, the launches had a very high sell-through close to 90% or higher:
2002-11-18 [GBA] Pokémon Ruby Version - 543,962 / 543,962 <89.79%>
2002-11-18 [GBA] Pokémon Sapphire Version - 549,337 / 549,337 <90.11%>
2004-01-26 [GBA] Pokémon FireRed Version - 517,874 / 517,874 <96.01%>
2004-01-26 [GBA] Pokémon LeafGreen Version - 495,245 / 495,245 <92.4%>
2004-09-13 [GBA] Pokémon Emerald Version - 790,527 / 790,527 <91.37%>
2006-09-25 [NDS] Pokémon Diamond Version - 820,047 / 820,047 <97.12%>
2006-09-25 [NDS] Pokémon Pearl Version - 768,687 / 768,687 <96.16%>
2008-09-08 [NDS] Pokémon Platinum Version - 963,273 / 963,273 <90.72%>
2009-09-07 [NDS] Pokémon HeartGold Version - 720,086 / 720,086 <91.16%>
2009-09-07 [NDS] Pokémon SoulSilver Version - 722,904 / 722,904 <91.48%>
2010-09-13 [NDS] Pokémon Black Version - 1,323,423 / 1,323,423 <89.21%>
2010-09-13 [NDS] Pokémon White Version - 1,234,356 / 1,234,356 <86.09%>
2012-06-18 [NDS] Pokémon Black Version 2 - 816,576 / 816,576 <82.91%>
2012-06-18 [NDS] Pokémon White Version 2 - 745,162 / 745,162 <77.43%>
With enough stock, I think X/Y could perform close to BW. So what we have to guess for X/Y is the same we for MH4: How many copies will be shipped.
Going by pre-orders (for instance, Amazon doesn't have any right now, only 3rd parties), I don't think the stock available will be similar to what was there for BW