The issue is simple.
Microsoft and Sony have a vested interest in 3rd parties software selling to boost the sales of their hardware and to get more royalties...
Does Nintendo need to 3rd party software to sell to improve hardware sales ?
That's not so certain, the Wii is already selling like hotcakes.
And the fact that the 3rd party landscape is so bare ensures every Nintendo title is a smash hit due to lack of competition...
Heck, if I was Nintendo I woudn't want things to change......