The lack of M/18 rated games from Nintendo are good for 3rd Parties

[Bodhesatva]

It goes both ways, though. You can say that Nintendo has left the market completely open for 3rd parties to capture the 15-24 male demographic; but you could also say that Nintendo's lack of strength in this area (They aren't completely lacking,  I don't mean that) means that some third party has to bite the bullet and be the first to expand this demographic on the Wii.

Put more generally, good first party titles are a double edged sword. They expand the demographic on that particular console, thus giving similar third party games an installed base to work from; simultaneously, they compete with and, perhaps, suppress the sales of those third party games.

So you're right, there is a good side to Nintendo's relative weakness in the violent, 16-25 year old male demographic. There's also a bad side, too, as third parties can't be sure that there games have an audience to sell to.