I respect your arguments, but for the above it doesn't really work like that. You have movies like twilight that grossly outsell movies like No Country for Old Men. The thing you have to remember is that there are many markets on one same platform. Those who buy Wii Music are not the same as those who buy Monster Hunter Tri, are even not necessarily those who buy a port of a PS2 game, like Bully. The problem with Gamecube as a profit base for 3rd parties is that it was limited. In contrast with the playstation 2, which ended up selling 141m I bevlieve, the GC only ended up with 21m (global, lifetime). When the Cafe launches, we don't know how it will fair graphics/performance-wise as compared to the other two, especially given sony's position that they don't want to do a huge push like they did with PS3. Add to that the fact that Nintendo still wants to sell its million sellers, it just wants to time them in synchrony with 3rd party dev launches so as to not eclipse them (from the Iwata interview, I'll provide source if needed), and you have a totaly different ball game.
Moreover, Nintendo was able to pass the 85m sales mark this gen, that makes it a very healthy base for 3rd parties, except for the fact that it doesn't have the HD power of the other manufacturers. With Cafe, that problem is gone, and so in my view, as a prediction, yes it will take time and 3rd Party Relations to get things going, but I see the conditions being right for proper 3rd party support, no matter how many people buy games like My Little Pony and such (they're different markets).
I get your point on the Wii Music/Bully comparison. And yes, crap movies do make money when good (even great) movies often barely eek by. (I'm also formerly a pretty big movie nerd, but I've pretty much abandoned my movie-love and vastly increased my gaming hunger.)
I'm wary of comparing sales of PS2 games to GameCube, however, and usually would prefer to compare GameCube to Xbox which had very close overall sales numbers (with the Xbox leading by a mere couple million). In that scenario, the Xbox still maintained better sales and support where 3rd party companies are concerned.
The Wii reaching 85 million should've been healthy for 3rd party devs but it still wasn't, except in rare cases. Hit franchises still struggled on the system. The casual audience doesn't seem to know a quality gaming experience from a throw-away iPhone app, so they didn't know to support, or expand to, what some of us would consider hardcore or "real" 3rd party video games. And the Nintendo fans... as is typical, pretty much just bought Nintendo stuff.
I do see how Cafe, with it's power roughly in line with PS3 and Xbox360 could manage some better ports of 3rd party games--like Call of Duty not being downgraded in any way, but I both see the support as slow to catch on, and quick to move away when the next Xbox and Playstation launch.
I firmly believe there are still treasures to be found in the Xbox360 and PS3's respective hardware, but I'm not kidding myself--while I love that this generation has legs (and it should), the limits of both systems will become far more apparent within the next two years. When Sony and Microsoft launch their next consoles, those limits will be left behind--except in Project Cafe--which will then be, last-gen tech.