I bet Nintendo will continue with the motion controls next gen, along with a cheap price for wii2 there will be less reasons to get wii1.  When wii 2 can do all that wii1 one does.  The competition is better this gen then last gen, which will cause wii sales to lower over time once the other consoles drop down to a more affordable price.  The wii so far is built better then the PS2, we all know how many people had to replace their PS2's. 

Major third parties supported the PS2 more then the wii, i can see the wii getting more/better games, but not on the level of the ones the PS2 had.

Well, you get two points with the PS2 replace rate and the third party support (PSOne to PS2 was a WINNER to WINNER succesor, GC to Wii was a LOSER to WINNER) because they were not expecting the Wii to be so successful.

But I really doubt Nintendo kills the beast early on its lifetime. Also, consider that Nintendo has yet to reach a sub-$200 price point, which they can reach... well... anytime they want. Right now, Wii's sale rate is higher than PS2's best days, that's why I consider it capable of beating it :)

About the competition... that's a highly subjective matter. I consider that the PS2 had a great competition last gen, but I don't know what you are referring exactly.

@Griffin
Well said, thats about the most well reasoned analysis I have seen on here for why the wii wont hit PS2 numbers

@ChronotriggerJM
Will you give it a rest for god sake. The philips CDi will never sell the kind of numbers that we are expecting from the CD32. Its out dated technology and a thousand miles away from the cutting edge AGA architecture

 In that case, a staggered launch for PS2 is no excuse. Sony simply could have increased production to launch their product simultaneously in all territories. They had the money to make it happen, but they like it staggered. They were being smart... ;)

I think the Wii gonna be the next PS2 in total sales and even myself as a fan of Nintendo don´t expected the huge success.