I see your point.
I'm kind of looking at through my eyes, and the eyes of the other people I know who either want or have a Wii (the haves are 2 lucky bastards).
The point I agree with you on, is people who may be disappointed in the single player aspect of the game because it isn't like the multiplayer.
If you like the single player game however, I don't see what hinders you from enjoying the multiplayer part? Yes it's different, but that's exactly my point it is different, they aren't changing the single player mode to fit the multiplayer part.
They are two aspects of the same game, for me it's like having two conversations with the same person. Like earlier today; At one point we were discussing past girlfriends and how that's going to affect our current(for me) future(for him) girlfriends. I said something to him about how one girl I dated a few years back didn't know how to use a computer, and then he told me he got a new laptop, I asked him if it the was one I suggested to him, he said yes, and we started discussing it's features, and other laptops, and other things, after exhausting that, we went back to girlfriends.
That's how I see the single player vs. multiplayer aspects of a game. The multiplayer branches from the single player, but it has no effect on the single player game, really the only effect it has to offer a break from the game. A break to stop being by yourself for a second and play with others.
When I had GC the only person I could play with was my brother, and every now and again one of my friends would come over, or I would bring the GC to one of their houses, but for the most part it PS2 all the time, because that's what all of my friends had. Finally, there is the Wii, two friends have it, the others except one, want it. I can't wait to not only be able to play against them, but not have to leave my house to do it.