Wii Fit will, without a doubt, sell over 40M, so GTA 4 x2 is obivous No doubt about it. Frankly, it should make ~ 60M. That's just short of GTA IV * 4. I don't think it will make x 4, but it will definitely make x3.
As for Platinum making the top 10...
Here's the top 15 for last year (guess who made it!)
1. Wii Sports - 17.5M
2. Wii Fit - 10.35M
3. MKWii - 10.43M
4. Wii Play - 7.85M
5. SSBB - 7.48M
6. GTA IV X360 - 6.33M
7. GTA IV Ps3 - 4.98M
8. New Super Mario Bros - 3.7M
9. Brain Training - 3.7M
10. MGS 4 - 3.55M
11. Mario & Sonic DS - 3.47M
12. More Brain Training 3.45M
13. MKDS - 3.45M
14. Mario & Sonic Wii - 3.3M
15. Gears 2 - 3.3M
And as SW is improving (a lot), we can safely say that you will need 5M +, and probably 5.5M + to make the top 10 (might even be 6M...)
Frankly - Pokemon Platinum won't make that. I really, really doubt it.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS
