It was an odd title for Wii, sure. But I think the issue is more that the publishers don't know how to reach the audience on Wii (which for sure will be much smaller than the total Wii install base) very well.
To sell something you need to reach who you want to sell to, and while I do believe the Wii overall has a smaller potential demographic for title's like this than the HD Twins I have no doubt the install base is big enough to support title's like MadWorld but I just don't think the marketing and sales messages are reaching enough people.
BTW what's with the Bayonetta comparison? That was a title that sold ok'ish on a platform (360) with a proven small demographic who are interested in such stuff, and ok'ish on a platform (PS3) where it had a better chance to sell but it's launch was badly harmed due to a lot of negative press (fair negative press for once) regarding the quality of the port.
MadWorld was a niche title that sold ok'ish but failed I think to reach the right awareness level with Wii owners to do better.
Try to be reasonable... its easier than you think...
