Sega Studio Director Constantine Hantzopoulos told 1UP that Sega will take a more cautious approach when it comes to mature titles on the Nintendo Wii. Last year they launched House of the Dead: Overkill, Mad World (pictured) and The Conduit. And although he noted that the typical sales curve is longer on the Wii (first three weeks aren't everything), Sega were surprised to see how EA failed to make something out of Dead Space: Extraction. That title was also said to be a test for EA when it came to mature titles on Wii.
Currently Sega has no adult themed titles announced on the Nintendo Wii so we'll have to wait and see if there are more coming in the future.