I think many people are putting too much blame on the userbase, rather than the games themselves. First let's take a look at the Wii 3rd party games that failed to live up to sales expectations

lol ).
Madworld- Black and White 7 hour beat-em up. I think the artstyle really put off people from purchasing the game. Madworld might have sold more on the 360 because of the novely of the chainsaw and gore, but I don't think it would've been a big enough difference to jump to a conclusion like "hardcore games on Wii don't sell!" Also to note, Madworld came out 2 days before Resident Evil 5. Which game do you think a hardcore gamer is going to spend their money on? An established brand or an unproven IP?
HOTD: Overkill/Resident Evil: DSC/ Dead Space: E - All railshooters. It's a niche genre There's too many of them on the platform, and the genre hasnt been popular for a long time. I don't see why anyone expected them to sell... maybe because of Umbrella Chronicles? Umbrella Chronicles sold based on brand name and on the success of Resident Evil 4: Wii Edition. I believe Darkside Chronicles failed to sell despite its brand because people were put off by Umbrella.
The Conduit - This game has the biggest chance of success, but reviews werent so good. The hardcore audience pays attention to reviews. If the game got 90's, I'm sure it would've done better than it did.
In all honesty, I think the game performed as they should have. Every Wii game that has been expected to sell by publishers has had a big negative working against its sales. It's either that the game was niche, had no advertising, or just flat-out sucked. I think the Wii is just like any other console, but 3rd parties have tried so hard to force an image upon it that many hardcore Wii owners have been put off by 3rd party games altogether. So when a non-niche fantastic game with tons of advertising comes out, I don't think it would sell as well as it would've before 3rd parties started pumping out so many cheap casual cash-ins.
Of course, a game like that hasn't come yet.
Closest thing I can think of is World at War for Wii, which sold signifcantly less than the HD versions. I think that can be explained by the fact that the COD series didn't become huge until Modern Warfare, which skipped the Wii. This was a huge oversight, in my opinion. While World at War sold well at around 1.5 million copies, it could've sold so much more if Modern Warfare Reflex was there with the HD versions Day 1.
Speaking of Modern Warfare Reflex, I believe that sold 500k in 2 months, despite having no advertising and releasing alongside the SEQUEL on the HD platforms. Pretty damn good for a hardcore game on Wii.:lol