Wii fit currently has a 27% attach rate, and will probably increase to about a 30-45% attach rate once supply issues are worked out, meaning that Wii fit has a very good chance of passing the GTA franchise once all is said and done

and its should be it's, your point...

All we need to know is that the wii will be the highest selling home console.

Its selling this much and hasnt changed much from when it began. No new sku and no price cut , and yet it sells like its christmas all year round.

Even if the wii falls off a little, all nintendo needs to do is just make colour varients or a price cut and it will beat the ps2 in no time.

I think it will outsell it, the reason for it to sell that much is that it appeals to everyone, not only the hardcore gamers, the kids like it, the parents like it, a regular guy will like it in a party, everyone like the Wii, I even miss it because it was really fun when we had people in.
Its a new way of playing games and being unique in its genre makes it something much more appealing to them that tried it.

I'm not sure if the wii will last as long as the ps2 because the ps3 was adopted very slowly and lost backwards compatibility. The next wii will have backwards compatibility i'm sure and will be more successful, at the very least it would start out well because of how well the wii did.

Even so i think the wii will outsell it, Nintendo will probably go with the wii for 6 years and it will likely sell similar to the next wii for the first year its out then die off quickly. The wii will probably be on the verge of outselling the ps2 right when the next wii comes out.

It doesn't matter if the Wii doesn't live longer than the PS2 does. It will pass the PS2's sales in a shorter time span than it took the PS2 to gather in the first place.

It will sell about the same as the PS2

 There is no logic behind that. The marketing possibilities for the Wii are endless. You can market to any age group, it just depends on how potent the airtime is to target demographic and the games that appeal as well. If the Wii was to exist for the same amount of time as the PS2 before being replaced based on sales without a price cut hypothetically even if it drops sales a bit it could outsell the PS2 by twice its sales based on its wide demographic base and near equal male and female installed base. This includes Children, Teens to adults and old people. It was marketed as a family system in the beginning. Just think what would happen if Nintendo made commercials focusing on individual demographics. I don't know how there is a failure to realize this.

The Wii2 won't eat up the Wii's sales, just like the PS2 didn't eat up the PS1's sales and the SNES didn't eat up the NES's sales. If you have 2 super-successful consoles in a row, they both sell a lot for a long time.