I really dont know what sort of sales they expected from those games. House of The Death is a on rails shooter and those games arent traditionally monster sellers, and sell best when on reduced price. It will reach soon 500k copies sold which is an amazing result, the Game is great it has humour, action. But it was never a big seller
MadWorld is a similar story, very brutal, over the top game with very unusual graphics for majority of Wii owners (and gamers in general). Good game but again with limited potnetial sales.
Havent played Conduit, so i cant judge it.
Overall if Sega wants sell millions on a Wii they need to produce games that can sell to wide group of gamers. Madworld and HotD will never be mainstream games that can reach milions, im sure if Sega decided to release Shenmue, Virtua Fighter or a Game like Bayonetta on the Wii it would've easily sell well.