Probably not this year (likely to lose to something like Gears of War 3), but in 1-2 years it'll probably become the best-selling game released in 2011:
-M-rated man-fest games for the PS3 and Xbox 360 (like CoD, Halo and Blizzard MMO expansions) usually have an explosive launch, but everyone forgets about them a couple of months afterwards.
-Nintendo games, especially Mario, Pokémon and Wii Fit *shudder* usually have good but not spectacular launches, but steadily sell very well over the years. Hell, Nintendo even predicted this back in 2009 when NSMB Wii had to compete with MW2 and, from what I know, NSMB's sold more copies than MW2 so far.
I remember, back in 2008, GTA 4 was what everyone was talking about. Now you can find it heavily discounted in various game stores, while the original NSMB for DS (an even older game) is selling better and for a higher price.
One other possibility is that B/W might be a fresh enough start for the series to re-launch a huge Pokémon craze like in the late 1990s, in which case they might even outsell Red and Blue! (Unlikely though.)
Yup, Nintendo's got the real power. Everyone's going to buy Gears of War 3 until Modern Warfare 3 comes out, and then they'll stop buying MW3 when the Halo remake comes out, and then they'll stop buying that when the Zerg expansion for SC2 comes out... (Actually, the Halo remake has a high chance of lasting a long time, considering that it's a remake of a game now considered a classic.)