There are many reasons why development costs are cheaper when developing for Wii.
Here are some:
Visual assets are less "sophisticated", meaning they take less time to develop and can be developed by less people (each person on the payroll has a base cost regardless of the length of their employment or productivity level).
Because the graphics aren't being pushed to the limits, existing engines can be used with out a significant visual or physics overhaul.
The novelty of the gameplay is what sells games on Wii (just look at the Wii's top sellers). Meaning a game can sell just from its core gameplay mechanic without the need for "depth" of hours of single player missions, story, etc. This means even less visual and design work, because the hours of gameplay come from mastering or having fun with a simple gameplay mechanic.
In a "traditional" (read: FPS, Action, etc.) game where there are lots of levels and single player areas, they are cheaper to produce per hour of gameplay. Some math, If you have five levels where the design (1 employee @ 40/hr) and the artwork (9 employees * 25/hr) takes 100 hours each per level (100 * 5 * (9*25) + (100 * 5 * 40)) would cost $132,500.
The same game on Wii would take less hours (lets say 80 per employee) and less artists (lets go with 3), (80 * 5 * (3*25) + (80 * 5 * 40)) would cost $46,000.
Shorter development time also means there's a competitive advantage against HD versions. Meaning less marketing cost.
Larger install base means that the advertising dollar goes further since each dollar will be viewed by more Wii owners.
Development Kits are significantly cheaper and less of them are needed because less people are needed.
Do I need to keep going?
So even by your (op) idea that a game could be worked on more by the company is irrelevant, it doesn't need to be to make a consumable product.
I would cite regulation, but I know you will simply ignore it.
