Isn't the Wii's installed base more than 2 times that of the PS3??? If the PS3 hits 20 million sales(if it ever does) there is no way the Wii will be at the same place. The Wii would probably be at 30 million sold at the LEAST.
A more realistic number would be 40 million wii's sold.
I honestly think the Wii's momentum is only going to get stronger this year. The most anticipated game for the Wii ever comes out in March. Smash Bros. Brawl. And I predict Wii Fit to be a worldwide phenomenon.