I don't usually jump into the blame game on the Wii 3rd party argument, but I think UbiSoft really dropped the ball here. They had a lot of good will with the first game, had a better received sequel, and completely disregarded it by not marketing it. Even worse, they released it on a day when Mass Effect 2 and TVC came out. From my perspective, it doesn't even look like they cared that they had a sequel to something that made them money.
Capcom's decision to market TVC really puzzles me too. There was no way in hell that game was ever selling anything. "Versus Capcom" isn't a franchise people rush to the store for, and Tatsunoko is a complete unknown. People were never going to care that this was a lot like Marvel vs. Capcom. The effort put into TVC- the extra characters, the online, and the marketing- it all shows that Capcom really cared about this title and wanted it to sell quite a bit. It makes me wonder why DSC didn't get an ad campaign though, when that was obviously the better choice to make as far as raising peoples' awareness. To me, it's as Sega advertising The Conduit but not Sonic and the Black Knight.
Which brings me back to UbiSoft: Tatsunoko vs. Capcom outsold NMH2? Really? With the kind of fanbase each series has on the Wii (nonexistent vs. healthy enough to make a sequel)? Talk about mismanagement.