http://www.digitalspy.co.uk/gaming/a136529/nintendo-aims-to-woo-hardcore-gamers.html
I love the fact that they mentioned two games for 2009 that they could have published themselves that could have helped even-out their family friendly image (by making it more of "something for everyone"). Well done nintendo.
I think they don't want to hog all the games, even if just as a publisher, to make third parties see that a good game sells. If all the good games are published by Nintendo then third parties will fail to see correlation and causation again and claim they succeeded because they were published by Nintendo, not because they were good.
Noone cares about "teh kiddy" anymore, now Nintendo is "teh granny". Third parties are more concerned about core games not selling than mature games not selling (which are a sub-branch of core games as most people who aren't part of the core market find the idea of virtually killing people abhorrent). This is much worse for them since while mature was a marketting gimmick, core is a design philosophy and they have no idea how to change their philosophy because it means suddently everything they knew was good is no longer valid and might even hurt the game. It's probably much easier for someone new to gaming to design a new market game than someone who has been part of gaming for so long that its conventions and goals seem natural and unquestionable.