Wii's "hardcore" install base abandoned the system long ago. I'm maybe halfway through the game and I'm loving it, but let's be honest, the last two years haven't been great for releases and the system has been tailing off.
Expecting a Zelda to do huge numbers on the system at this point in its life is like expecting FFXII to break records if it had been delayed into 2008 and still released on PS2.