I don't agree with this. Just go to your nearest EB store and check the Wii/Wii-U and even the 3DS library. A lot of it are these sorts of games:
http://www.cravingthesavings.com/ima...110509wii2.jpg
This is what I am calling Baby games because they freaking are. A good game doesn't have to be FPS (Boring!) or dark and gritty. It just has to be enjoyable for people above the age of 6.
Nintendo does have great games but they get released once in a blue moon and most of their franchises are not 'gritty' or FPS and still good with wide praise from hardcore gamers. We need more frequency of decent to good game that anyone would want to play - That was what made the NES and SNES so successful. As you mentioned, when they begun to move away from that, a gradual decline occurred and we are witnessing it's impact today.
Just so you know, Nintendo publishing games in non Nintendo platforms is not unheard of. Not counting the CD-i abortions, there were a series of Mario educational games for PC.