Wow... so many things to say, so little space in the box. 
First of all, raw sales alone will not determine which platform a developer supports. The real number that will determine if a company continues to make games for a system is the profit made. And it's a fact that it cost significantly more for a company to make a PS3 game than a Wii one. Most estimates give the Wii an advantage of half to a third of the costs of a PS3 game. And by looking at a few of the games out there, I bet even less than that. (I'm looking at you, Cooking Mama!)
Using a conservative ratio of half and assuming that the net profit on a Wii versus PS3 title is the same on a unit basis (after licensing, manufacturing, advertising, etc.), Wii titles only need to sell half as many copies to be profitable. And I bet many of the Wii 3rd Party games have made a tidy sum, while few PS3 ones have in just Japan. And why are we focusing on just Japanese sales anyway? Video games are global. Publishers care about how well their games are going to sell worldwide. While Rayman only sold 14,250 copies ltd in Japan, I bet Ubisoft is thrilled with the global sales that probably top 400,000.
Another reason for the lack of third party sales is the quality of the titles and who the system appeals to. The Wii doesn't have a top notch racer like Ridge Racer 7 or a fighter with the pedigree of VF5. I bet if there were some better games, they'd sell more copies. And many people have been drawn to the Wii by Wii Sports. They're picking up Wii Play for the extra controller and cheap game included. Once they get their fill of those, I'm sure they'll be back for something else.
In the end, there appears to be a shift of software development to the Wii. Will it last? Only time will tell. Hopefully those moving over will bring some good games. Otherwise, they can stay on the PS3 or 360.
Before I go, I'd like to give props to OriGin for a great post. Thanks for giving us all the numbers and not cherry picking the ones to support one side or the other. 
Numbers are like people. Torture them enough and you can get them to say anything you want.
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