Blood and narratives where every other word is of the "4-letter" variety aren't exactly commonly loved themes, and I have to say that I'm fairly certain that the primary demographic for that stuff isn't exactly a match-made-in-heaven for the Wii.
Some people love that stuff. Most don't. Put it on the family-friendly Wii -- effect exaggerated. The numbers seem completely logical to me.
I actually think it'll do decently, lifetime. Like 300K or so. That's not bad, considering its environment.
I personally love the genre... I even liked Golden Axe: Beast Rider, and Conan, as well as the recent Wii Rygar. MadWorld? Nope. Not worth my time. Yeah I know it got good reviews. I'll watch Heavy Metal again, instead. More appealing to me, for some reason.