Well, this is certainly interesting.
Today, Nintendo added to the WiiWare section of the Shop a "channel" specifically for promoting Metroid Prime 3. There are two new videos available, with at least two more on the way (coming on the 13th). The news section of the Shop carries a link-tagline of "A month of Metroid!" leading me to believe they will be promoting the game, through the Wii, for the rest of the month.
It's a bit late in the game for advertising, but it is an admittedly cool concept.