Spak, the problem, I believe is in the variety of mature games. The fact of the matter is, there was never any real effort to have mature titles on the 'Cube by Nintendo. If there was, then they wouldn't have made all the massive f*ckups that they did (like the purple color, shape, statements about neutrality). The games you listed are great, beautiful, and a step in the right direction, but they are spaced far apart. Getting rid of Rare and SK and 'cramping their style'/micromanaging (ala Michael Eisner? Probably not that bad) didn't help either.
Plus, the blockbusters are more 'everyone-games' than '17+games' in terms of content(except Geist), though not necessarily difficulty or skill. What needs to happen is that after the release of Metroid Prime 3, Retro getting back to those early abandoned projects from before the restructuring and layoff Nintendo IPs for a bit. That'll help a little bit, but what is really needed is steady third-party support. I think Nintendo has worked on alot of its image problems in terms of the design of the console, and having MP3 and Zelda at launch couldn't hurt that image. But those games alone aren't enough to compete.
People who live for M-rated games can't wait on Nintendo to bring them, which is why third-party devs who make those kind of games are so crucial.