At the moment I could understand a certain level of resistance for a company to spend a lot of money developing an exclusive "Mature" title for the Wii, in particular a Japaneese company producing a "Mature" title for the Wii; so far the Japaneese audience has not (really) bought any non-family friendly games for the Wii, and in the rest of the world sales have been (reasonably) poor due to the majority of those games being ports or poor quality.
Now, games like Manhunt and Resident Evil: Umbrella Chronicles (if they're well executed) will likely sell moderately well in North America which should demonstrate that there is a certain interest in these games; if a Wiimake like Resident Evil 4 does well (for what it is, say 250,000 to 500,000 worldwide) you may see other companies test the waters and Wiimake PS2/Gamecube/XBox "Mature" games by the end of the year.
In the long run I think that you're going to see Konami (and other developer) eventually producing "Mature" games for the Wii because as its userbase aproaches 20 to 30 Million users there will be a large market for these games.
