The biggest reason for the Wii's dominance is Japan. While Microsoft only sold 0.43 million consoles in Japan yet, Nintendo already sold 3.46 million Wii's to the Japanese people.
So far no official numbers have hit that have the Wii past its Microsoft rival, but Vgchartz.com's own homebrew numbers, gleaned from retailers worldwide, project the Wii is slightly ahead at 10.57 million consoles sold, compared to the 360's 10.51 million. These numbers are meant to project consoles sold, not consoles shipped, which gives the sold out Wii a slight edge. There's no telling when we'll get official numbers to know all this for sure, and the 360 still has a comfortable lead over the Wii in both Europe and the States, but it's looking like we'll have a new market leader in town soon enough.