An interesting insight from a Slashdot thread on the Nintendo Wii and its prospects, made by a gentleman named John Hu/mmel, aka "Dark Paladin" (awesome):

it would appear that Nintendo has a lot of 3rd party support time time around, which made me think of why, and then something that Ubisoft president commented on made me figure it out.

Long story short, he made some less then flattering remarks about the PS3 — how it just ups the power. The same could be said for the 360. But that's no the issue for a publisher; for a publisher, all of that extra power and HD requirements goes into cost. Now, a development team needs even bigger hardware, a bigger graphics and sound team to get the same game out, which now increases the cost of the game by a large margin - say from $1 million to $7-$10 million. For a publisher, that means increased risk, reduced margins, and relying ever more on "certain" hits (which can vanish if something goes wrong — look at the Tomb Raider franches, and what they've had to do to get it back).

Nintendo is offering publishers something more than just a gimmick: they're offering them reduced price. Look at "Brain Age" - developed, tested, and ready for market in 90 days, and it hardly needed a graphics team. Since the Wii uses really Gamecube development systems with more power, that's an easy transfer of knowledge, which is why I predict that for the first year, Wii games will look pretty much like Gamecube games, maybe a little smoother.

But for the publisher, once you get past the controller issue, it's reduced cost, reduced time, reduced risk over time. If the Wii takes off at all, it may be that publishers wind up favoring it if for no other reason than it makes them more money over time.

Another commenter follows up:

Your numbers are a little off. My understanding is that a XBox/PS2/Gamecube title costs $8 - $12 million to produce (with some AAA titles going into the 20s), and last I heard HD games were expected to at least double the costs. (Is it any wonder publishers are afraid to take risks with money like that involved?)

...

Yes, sure, it might take more people to program a game for such a complex controller, but you aren't going to need 200 people churning out high res textures that will only be appreciated by people with HDTVs. Nintendo knows what it's doing.

Makes sense to me.