The Wii wil never get the kind of third party support that the PS2 had.

[TheSource]

Its very simple really for third parties:

If a game is going to sell 5 million units, it is best to put it on 360/PS3. Even if costs $30 million to make, and $ 5 million to advertise. A non-liscense based game will get $35 out of $60 roughly. 5m * $35 = 175m - $35m = $140m profit. Something like Mario & Sonic would be $22 out of $50 * 6m on Wii against maybe 12 million development costs... only $120m profit .

If a game is going to sell 2 million units and cost 35 million, it should still be on 360/PS3...  $35 * 2m = $70m - $35m = $35m.

A high profile game selling 2m on Wii, with development costs of 10 million, and ads at 5m... $22 * 2m = $42m - $12m = $30m

There is less risk for losing a huge amount of capital on Wii (no $20-$30m game dev costs), and less risk for breakout success on Wii as well. But Wii is a great platform if your one of the many developers who can make a game which costs $5m and needs to sell only a couple hundred thousand units.

It goes like this roughly -

0-100k: Probably not profitable anywhere

100k-150k: Usually Profitable on DS, occassionally profitable on PSP/PS2, in rare cases profitable on Wii

150k-200k: Profitable on DS, usually profitable on PSP, sometimes profitable on Wii/PS2

200k-275k - Profitable on DS, PSP, usually profitable on Wii/PS2, in rare case profitable on 360/PS3

275k-350k - Profitable on DS, PSP, Wii, PS2, sometimes profitable on PS3/360. DS sweet spot ($15 * 315k = $4.7m - $1.5m costs = $3.2m profit. PS3/360 - $35 * 315k = $11m - $10m = $1m.  Wii - $22 * 315k = $6.9m - $4m = $2.9m)

350k-650k - Wii/DS sweet spot (500k * $22 = $11m - $5m avg costs = $6m Profit), PS3/360...not so much (500k * $35 = $17.5m - $15m = $2.5m Profit) DS  (500k * $15 = $7.5m - $1.8m = 5.8m profit)

650k - 1350k - Wii - (1m * $22 = $22m - $6m avg costs = $16m Profit), PS3/360 ($1m * $35 = $35m - $20m = $15m profit), DS (1m * $15 = $15m - $2m = $13m profit)

1350k-1650k - Wii (1.5m * $22 = $33m - $8m avg costs = $25m profit), PS3/360 (1.5m * $35 = $52.5m - $22.5m = $30m profit), DS (1.5m * $15 = $22.5m - $2.5m = $20m profit)

Essentially, above about 1m units it just makes more sense to make more titles for PS3/360 on average. DS/Wii allow developers to be profitable at higher thresholds at lower sales levels, while PS3/360 allow developers to be profitable at higher thresholds at higher levels. But with Wii/DS you still make alot if your game sells 1m, 3m, 5m copies. For PS3/360 you can't make money below 275k 90% of the time, and in many cases it makes more sense to develop a title for Wii/DS until you know it will hit 1m. So for Wii you can make money from 175k (if your real stingy as a developer) upwards, DS up from 100k. But in most cases its probably 100k/250k/400k as the magic numbers.