It seems like you're saying that proper marketing is a necessary (although not sufficient) condition. I can mostly get behind that idea, and would add the example of Brain Training in the U.S.: it bombed in the first few months, until NCL twisted NoA's arm and made them advertise it. The result is millions in sales.
But there do seem to be a few games that defy that. Bethesda didn't advertise Oblivions very much, for instance, but it still did great at retail. Corruption saw little marketing power thrown behind it, but it's still gone platinum with ease. RE4: Wii Edition is another example.
However, those titles are all from established series, so the lack of advertising probably wasn't as fatal as it would be to newer games (and including advertising may well have helped them sell even better). But there a few IPs that tell the opposite story. I don't think Smarty Pants was all that well advertised, for instance, and it was a new IP, but it's gone platinum (with change). Game Party became advertised, but only after Midway realized that it already had a hit on its hand for something it knew was shovelware. The original Cooking Mama was also a surprise hit, one that wasn't advertised until after it became mainstream.
But all of those examples seem to be the exception, rather than the rule. In general, you're right that people simply won't buy games that they don't know exist, and the bigger a game's budget the more hellbent the publisher is on letting people know that the game is out.
In fact, we already know that most publishers deliberately allocate about a tenth of a title's projected revenue for marketing purposes. So the more expensive games will get more advertising. And we all know that 360/PS3 games are far more expensive than their Wii counterparts. So is it any surprise which games are marketed more than the other?
Despite all of this, I still do think that the Wii's demographics are different than that of the HD consoles (albeit by nowhere near as much as they had been just a year earlier). And while I laugh when people say that third-party games don't sell because people only buy Nintendo games, I do agree that many third-parties still don't completely grasp the Wii's audience.
I'm not saying traditional titles don't sell on the Wii (we know they do), but stepping back a bit, I'm struck by how the Wii has created several games that have sold far better than they were expected to (Carnival Games, Game Party, the light-gun games, etc.), whereas the HD twins don't seem to have so many happy surprises under their belts.
That is to say, third-parties are occasionally disappointed in their HD titles' sales, but they rarely find a surprise hit on their hands: they know what does and doesn't fly there. They also have Wii flops, mind you, but we've seen several occasions where they unexpectedly found that the Wii audience likes a game that they just shoved out there.
The Wii remains less familiar territory for everyone, including Nintendo to an extent. But I think you're mostly correct when you remind third-parties that "he who has a thing to sell, and goes and whispers in a well, is not so apt to get the dollars, as he who climbs a tree and hollers."