I'm part of the Wii casual-gamer demographic -- a 48 year old man who hasn't owned a console since the Intellivision and never gamed on my PC. I bought it mostly for Wii Sports. According to analysts, I a) won't buy many more games and b) if I do, they'll be Nintendo games.
I was just looking over the games I bought since I got my Wii a few months ago. I have two from Nintendo: Link's Crossbow Training (which came with the Wii Zapper) and Wii Fit.
The other games I've bought so far are:
Pinball Hall of Fame (Crave)
House of the Dead 2 and 3 Return (Sega)
Resident Evil 4 (Capcom)
Mercury Meltdown Revolution (Ignition)
Zack & Wiki (Capcom)
Sonic and Mario at the Olympic Games (Sega)
The Godfather: Blackhand Edition (EA)
Rayman Raving Rabbids (Ubisoft)
Dance Dance Revolution Hottest Party (Konami)
We Ski (Namco)
(Side note: most of them I picked up on sale at either Gamestop or Amazon. Wii Fit and DDR were the only ones that were $50 or more. The rest ranged from $30 to $14.99.)
My not particularly astounding conclusions: some of us casual Wii buyers do move beyond Wii Sports and there are quite a few playable third party games out there. Also, I'm cheap when it comes to buying games... $50 just seems pricey to me (maybe that's part of the casual demographic).