Does something actually sell better just by virtue of being released on Black Friday? Do Americans only want products released on that exact day?
I think Wii would sell either way. In fact, history tells us that Xbox outsold GameCube slightly in their first holiday season, so it would seem that it's better to launch earlier. Of course, that's a pretty narrow perspective, but the point is that, based on the Xbox and PS2, it doesn't hurt to launch a console before Black Friday.
We do have a peak shopping period in Canada, I think it's some weekend between "Black Friday" and Christmas. I don't really remember, but I do remember hearing that a predictable top-sales weekend exists.