I believe that the only way that this is possible is if they have either increased production by a bit or divert some supplies to North America for game releases (most likely the Super Smash Bros Brawl release coming up in a couple of weeks).
They probably will not be able to divert units for Wii Fit and Mario Kart releases (if the release dates for those don't change) because of the fact that European (Kart, Fit) and Japanese (Kart) releases for those games are most likely going to end up being close to the U.S. release dates (that is if release dates don't change).
While it is possible for the Wii to catch the 360 by June in North America, I believe it will probably end up being a little later. Also, remember that this is only for North America (saying that the Wii has already passed 360 in some other territories - especially Japan).
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They probably will not be able to divert units for Wii Fit and Mario Kart releases (if the release dates for those don't change) because of the fact that European (Kart, Fit) and Japanese (Kart) releases for those games are most likely going to end up being close to the U.S. release dates (that is if release dates don't change).
While it is possible for the Wii to catch the 360 by June in North America, I believe it will probably end up being a little later. Also, remember that this is only for North America (saying that the Wii has already passed 360 in some other territories - especially Japan).