I think you're creating a fallacy when you pretend that a niche-fuck game like MadWorld has as much sales potential on Wii as like a new GTA/CoD would on 360.
Bayonetta will probably do better but it won't be because of some demographical rift between the Wii and the HD consoles, it's because mainstream gamers will be more receptive to it. It's still not going to do too well though, I don't think.
Also, publishers looking at something like Dead Space or Darkside Chronicles to determine their game plan is completely illogical. Let's say Jimmy goes to school and aces his test. Well, the school doesn't believe that he's smart enough, so they give him the same exact test again the next day. Jimmy is pissed about the school underestimating his intelligence, so instead of filling out the test again he just draws a giant dick. Does that mean that Jimmy is stupid? No, he's just annoyed about having to do the same shit over again, which is perfectly understandable.
I think those games not doing so hot reflects a more thrifty base of gamers than their sales potential. Look at how the GTA DLC did when it was released on a disc. Halo ODST did fantastic but not as great as Halo 3. This isn't at all because Halo and GTA aren't profitable franchises, that'd be silly to suggest. It's because the perceived value of those games is lower than their predecessors. Just like how no one wants to buy RE:UC 2 when they already played RE:UC, not to mention that light gun games isn't exactly a popular genre. The # of Wii rail shooters is pretty disproportionate compared to other consoles.
It's even harder with new IPs because gamers are going to be less willing to plop $50 for The Conduit or No More Heroes than they would for a game from an established series. And unfortunately for Sega, they really don't have many successful, established franchises outside of like Sonic and maybe Monkey Ball that they can count on. Which results in another epidemic of sorts where publishers will have a moderately successful game and immediately try and turn it into a cash cow. Capcom for example - Oh, Viewtiful Joe did okay on the GameCube? Line up a sequel and contract a Saturday morning cartoon, stat! This is going to be the next Pokemon!
I think the best strategy right now for Sega would be to reboot Sonic, Monkey Ball, and some of their older properties (Phantasy Star, Streets of Rage, NiGHTS) across all of the major platforms and try and re-establish their credibility before branching out. This doesn't apply specifically to Sega, most publishers could learn from that.
Fuck I'm tired of typing.