I've been a Nintendo fan all my life and the vast majority of the games I own for all Nintendo systems are indeed first party.
That's another reason why I won't buy it at launch unless they have some good launch titles available; if it's nothing but third party stuff, I'll hold off. That's what kept me away from the 3DS until the price-drop, and the only game I have for the 3DS is OoT.
I don't care much at all for third party support on Nintendo's systems...well, I do, because it helps keep them afloat and there's the occasional third-party game that I actually want for a Nintendo system, but they're lucky enough to have the amazing first-party lineup that they do. I care about third-party games on my ps3, for example, because it's a much wider market. But you can count on Nintendo to have the best all-around first party lineup at the end of the day, even if they get off to a slow start.
The way I see it, it'll take developers a bit of time to get a handle on the Wii-U anyway, meaning the initial games won't likely be top-notch. I'm guessing the touted features will feel forced at first and gradually expanded upon. Nintendo has a great grasp on their technology, but it always seems to take developers a fair amount of time to churn out the good games, save for a few. So unless there's a new Mario platformer, Zelda game, or smash bros available at launch for the Wii-U, I'll steer clear until something comes up.