Good games are supposed to sell well. Unfortunately, this is proving not to be completely true on the Wii, leading 3rd party developers to produce high quality games on other consoles. A simple analysis follows that shows this effect.
The average of the top 10 selling 3rd party games on each platform are listed, along with the average metacritic score:
Wii: 3.40 mil / 65.6
PS3: 4.01 mil / 90.1
360: 5.81 mil / 89.1
A few key points: Despite the largest userbase, the top selling 3rd party titles sell less on the Wii than on the HD consoles. The PS3 and 360 have high metacritic scores of around 90, signifying that the owners of these consoles tend to purchase better (reviewed) games. Finally, the average score for the top 10 selling Wii games is actually almost the same as the 50th percentile score for all Wii games. Essentially, there's no difference between the average score for the top 10 selling Wii games and the average score for ALL Wii games released.
Next, the average of the top 10 scored 3rd party games on each platform, along with their corresponding sales:
Wii: 88.6 / .69 mil
PS3: 93.5 / 3.17 mil
360: 94.5 / 4.69 mil
The first point is that higher quality 3rd party games tend to release on the PS3 and 360, as their top 10 metacritic scores are 5-6 points above the Wii's. Comparing the metacritic scores / sales of the top 10 rated vs top 10 selling games on the PS3 and 360 shows there isn't much discrepancy between their sales/scores: high rated games sell well, and high selling games are rated well. When the same comparison is made for the Wii, it's clear that games that are well reviewed obviously do not sell well.
This seems to confirm that developing on the Wii is almost a crapshoot. Selling well on the Wii does not correlate to quality: spending money to produce a high quality Wii game is not a good investment. Clearly, 3rd parties have already picked up on this and are shifting their strategies accordingly.
It's difficult to justify thinking spectacular 3rd party Wii games will sell well when there isn't any evidence to support it.