It's definitely possible. PS3 is selling better than PS2 at the same point (heard this too many times; not going to check) and that's at a higher price. MS has a problem: they don't attract casual gamers. Nintendo has a problem: Wii isn't very powerful. However, while Nintendo has a problem we don't know how big one it'll turn out to be. Right now it's not a problem but it might become one when PS3's price falls to $200 or something else that's good enough.
At this pace PS3 might actually reach 150M. However, there's one thing: which one (PS3 or Wii) will win when PS3 has a decent price? We don't really know. Wii could continue dominating casual market. PS3 could win back PS2 users. PS3 could start dominating the casual market. We can't be certain; we can only guess. This could be when Wii's lack of power might come in; or it might not.
Anyway, Wii's not going to last without something big and I don't mean games. When Wii's out, either its successor or PS3 will start (or continue, depending on what has happened) dominating. I think it's going to be PS3 but it's a bit hard to predict.
Oh, and I don't believe Wii and PS2 have too much common user base. Wii is getting new consumers to play; PS2, I feel, has a slightly different target. I could be wrong here, though.