"I think what they're waiting for is someone to show them a successful game concept on the Wii so they can copy it."
That's an interesting idea. Somehow the third parties aren't bringing over the "good games" -- good games that are simply good games regardless of the platform. On top of that, they're not even cloning those "good games" in some form for the Wii (at least in the volumes seen on the other platforms).
On the opposite end, select game makers have been releasing games Ian might view as "half-efforts" that have achieved moderate or greater success despite not being triple-A mega-big-budget blockbusters, whether ports or original, including the likes of: No More Heroes, RE4 Wii, RE Umbrella Chronicles, Okami, Boom Blox, and recently Tales of Rehash: Dawn of the Casuals -- these titles get some attention for simply helping to flesh-out the software library, yet other game makers haven't budged to help fill in the gaps. Sure, Nintendo's perceivably traditional games have been leading the pack in sales, but third parties can't really make the excuse their mega-million blockbuster games can't compete since they have yet to even try -- if traditional "gamers like Ian" are only willing to purchase triple-A third-party games, then sales of the comparatively less successful "half-efforts" cannot reliably predict the performance of a would-be mega-budget-blockbuster and should not determine the release of such mega-budget-blockbusters. (arguably, it would be stupid to gage things that way, but that's the vibe I've gotten from third parties since launch)
Assuming the game makers aren't stupid, are they just SLOW? Maybe they're still taking time to understand the sales dynamics of the audience (see: Boom Blox sales warming up over time, rather than tearing up the charts on release)? Taking time to rethink their platform targeting strategy? One can argue that waiting this long is BAD for the publisher, as they watch the world's cash ride Crystal Caravans into Nintendo's vaults. It's a fact of life that percentages of the customers who gobble up the Mario Galaxies, Smash Brothers, and Karts will look at other games to supplement their game library; but one might not even get the impression third parties are getting their foot in the door to fulfill that purpose.
To be this slow, and without silly conspiracies, maybe they're stupid after all? or just painfully, profit-bleedingly slow