My guess is well because they sell for long periods of time.
These 1st Party games sold like crack and still sell decently
Super Smash Bros Brawl
http://gamrreview.vgchartz.com/sales/6962/super-smash-bros-brawl/
Super Mario Galaxy
http://gamrreview.vgchartz.com/sales/6963/super-mario-galaxy/
Mario Kart Wii
http://gamrreview.vgchartz.com/sales/6968/mario-kart-wii/
And these 1st party games tapered off. By now they are discontinued
Big Brain Academy: Wii Degree
http://gamrreview.vgchartz.com/sales/2906/big-brain-academy-wii-degree/
Metroid Prime 3
http://gamrreview.vgchartz.com/sales/6969/metroid-prime-3-corruption/
Wii Music
http://gamrreview.vgchartz.com/sales/6969/metroid-prime-3-corruption/
The bottom line is, Wii games still sell and profit for Nintendo. Wii games sell longer and have longer legs than PS3 and 360 games, but there are notable exceptions (se LittleBigPlanet).
SOCOM; Confrontation
http://gamrreview.vgchartz.com/sales/26690/socom-us-navy-seals-confrontation/e
As you can see, the sales have fallen off, after a short time.
You do have a point though they need to slash prices or bring out player's choice. (SMG and SMG2 were both 40$ at my Wal-Mart)
