DarkSiders, Saints Row, UFC, Homefront, De Blob and Red Faction are their big names at the moment. They make good (But not AAA) games, but I'm not sure they could pull of the cross-over appeal type game Nintendo craft.
This all reeks of Just Dance mark II for me, a random Wii game coming out of no where and capturing massive sales off the Wii market. It appears innovative and original ideas can lead to huge payoff on the Wii, albeit it's still early days to get carried away. Here's hoping if it does make it big, THQ don't go overkill with games and kill the thing off a la Guitar Hero.
I think you might be underestimating how the announcement of this device was received, and how well THQ anticipated it doing. I seem to remember quite a few sites and magazines thinking THQ was going to be on to a winner with this, and they themselves regard it as a long term peripheral that should sell in the millions (a soft launch with limited stock may just have been business prudence, since expectations aren't always met - better to have to produce more stock because something is the success you thought it might be than to have a load of expensive stock gathering dust because you misjudged the market).