It has a great chance due to the Wii's much larger userbase. However, if it (or Mad World in its turn) follows the pattern of games like No More Heroes, Zack and Wiki, and Metroid Prime 3, it won't. The question is can the Wii with its large casual base and following be a system that sells games in more traditional genres that well, and really only five games out of over 200 plus Wii games have managed to sell anywhere near the Wii series games -- Mario Galaxy, Mario and Sonic at The Olympic Games, Zelda: Twilight Princess, Mario Kart, and Super Smash Brothers.

Hypothethically yes will it no

You have to remember that Metroid Prime sold really well because people thought it was a much different game than it was ... They expected a first person shooter and what they got was an adventure game in first person with shooter elements. This was one of the reasons why Metroid Prime 2 sold so poorly in comparison.

Now, Metroid Prime 3 has outsold Metroid Prime 2 and continues to sell every week ... It has currently passed 1.5 Million and by the time it is done (after it is a bargain priced game for a couple of years) it should easily pass 2 Million in sales. Other games like Resident Evil 4: Wii Edition, Resident Evil: Umbrella Chronicles, Star Wars: The Force Unleashed and Red Steel all demonstrate that there is a market for games that target the same demographic as The Conduit.

One problem with stating whether it will or will not sell as well as Killzone 2 is that we don't know how well Killzone 2 will sell ... As I said in an earlier post, Killzone 2 has to face direct competition from FEAR 2, The Chronicles of Riddick, and Resident Evil 5 which are all much better know IPs that have a far better track record for quality and could easily steal quite a few sales away from Killzone 2.

Hypothetically, yes it does have a chance.

If every PS3 owner purchased Killzone 2 and every other Wii owner purchased The Conduit, than The Conduit would outsell Killzone 2. There is the answer to your hypothetical question.

Will it happen? Most likely not.

Killzone 2 doesn't have to be good to sell well. The game is being massively hyped, set to be advertised well, and will be incredibly front loaded.

Wii games have historically not had huge launches. Thus Conduit would have to sell over a period of time. Conduit is more pressured to be a good game.

The only advantage Conduit has is userbase size and less competition.

I see Killzone 2 hitting a little over 3 mil while Conduit pushes out 1.5 mil.

It can. But it most likely won't.

If Call of Duty: World at War can't sell well, why would The Conduit?

There's almost 50 million people with a Wii. I think it can do it.

World at War can be purchased on the XBox 360, Playstation 3, Playstation 2, Nintendo DS, and PC.

     If Killzone 2 sells as many copies as Uncharted or Resistance I (2.52 million and 3.49 million copies sold respectively), and The Conduit sales no better than all of the Wii games you mentioned:

Resident Evil 4 Wii Edition 1.76 million
Metroid Prime 3 1.49 million (It will probably pass 1.5 this week, but this is what the site currently gives it)
Resident Evil:  The Umbrella Chronicles 1.33 million
Star Wars:  The Force Unleashed 1.08 million (The PS3 version has sold 1.07 million even though the PS3 has a userbase less than half the size of the Wii's and it is a Star Wars game, so what does that say?)
Red Steel 1.08 million

then Killzone 2 should pass the Conduit.  However, my gut feeling tells me that The Conduit will do 5 million for some reason, and I don't think Killzone 2 is going to do as good as some hope.