Because too many people answer with their fanboyish feelings not actual logic.
The actual logic shows that Animal Crossing or Gears 2 have the best chances of being #1 LTD.
Then you have the wild card of Wii Music, which I personally think it will top out around 3m, similar to LBP.
A logical person would realize the LBP is hitting a subset of hardcore players. Not a mainstream game which is basically required if it expects to hit >5m.
Now, you could argue that AC is similar, but, it has already proven that as a IP it can reach 10m, and the Wii has a lot of DS crossover.







