on first thought ps2 had a 80m userbase when gta:sa came out (i think) so it might be more difficult. I think everyone that was pumped for it has already bought it. The one big problem is that wii has already outsold all its predecessors, and it's last predecessor by double, and it will be hard to get those people who are longtime fans of nintendo games because the base just isn't aware.
think about it to hit the record it will have to sell 12 or so million. that's about 2/7ths of the people with a wii.
people on the gamecube bought double dash at about a rate of 1/5.
it could be close, but unless they bundle it, or already have it bundled it might be difficult.
@fernando- wii sports is not the best selling game. it is simply the game most wii owners have.
