No, the reason he, and I think that KH3 will be on PS3/360 isn't because of fanboyism (don't you own a Wii, anyways? After all, you have a friggin' Miyamoto quote in your sig)
Some of us believe KH3 would go MP 360/PS3, because *gasp* it might sell better! It's not fanboyism, it's a strong belief that it could. Spiderman, Shrek and POTC all sold far far better on PS3 + X360 than the Wii alone, and if that represents the fanbase that'd buy the Wii KH3, then even there, it proves that the fanbase of the Wii wouldn't quite be as strong as you think.
Like it's been said, KH1-2's sales, the vast majority, were in countries where the 360/PS3 are the strongest. Not only this, attach ratios for the PS3/360 are better, therefore more software is being moved, and a greater chance of selling KH3 to the purchaser(s) of the PS3/360.
Again, IMO, I'd think there will be a KH for Wii, but probably like FF:CC was. It'll probably be a spin-off ala FF vs. XIII.
Don't say your fanboyisms don't get into the argument, and only ours does.
As I said it's a non-issue for me personally as I will own all the platforms. But, first of all your entire argument rests on one basic and completely wrong principle: That Square Enix will EVER release a dual platform game on a primary franchise. Since the NES days this hasn't happened, and I don't know what you think makes the Xbox 360 so special that they will do this now, other than the fact that you own it. So that's why I think your personal preferences are getting in the way of your logical analysis of it's likely location. It will be PS3, Wii, or 360. It's not going to be 2 platforms just so it can compete with the Wii. If Square Enix feels that they would have to make it 2 platforms to sell well, guess what they'll do? They will put it on the Wii.
Oh, and now you are making up things to try and win this argument, which is incredibly insulting. Shrek the Third wasn't even released on the PS3, and it sold worse on the 360 than the Wii (did you think I wouldn't check on a site where they are 1 freaking click away?) http://vgchartz.com/games/game.php?id=6121. http://vgchartz.com/games/game.php?id=6120. Not that movie games are at all relevant to a Disney/SE RPG, but if you are going to lie about numbers I'm damn sure not gonna let it slide. Pirates of the Carribean and Spider-Man 3 have nothing to do with Kingdom Hearts (Hell, even Shrek is a HUGE stretch).
So, moving past fake numbers, you have yet to state a reason that movie game sales determine a Disney RPG's sales... That's like saying Wii Sports shows that Halo 3 would sell better on the Wii. They are completely unrelated. The strongest sales for Kingdom Hearts were in America and Japan, the weakest in others. Now correct me if I'm wrong, but are the Wii's strongest sales regions not America and Japan? Please tell me if I got that wrong, but you're going to need to change the numbers on the site too...
Attach ratios for the PS3's are worse in America (3.4 to 3.6) and HORRIBLE in Japan (1.9 I believe). The 360's were slightly better than the Wii in America, and of course it's a non issue in Japan (basically balancing the 360 out to being a horrible platform for KH).
So, let's review:
You think that Square is going to break a 20 year trend of no dual platform games for their primary franchises, so that you can play it on the 360. You site movie games as the reason (with one of your examples complete BS), and higher attach rates in the countries that it sells (which isn't true at all). I'm sorry, but the only situation I see of KH3 not being on the Wii is if development began more than a year ago. Otherwise, the spinoff will be on the PS3, and the 360 will probably get nothing (they aren't going to sacrifice 1.2 million Japanese sales for the 360 to get the game).
Edit: Heh, this was just posted. Figure I'll add it for reinforcement against your attach rate argument http://www.vgchartz.com/forum/thread.php?id=3795&start=0#end