For the most part the core gamers sites are losing love for the Wii because they know that Wii is just not for them anymore. Most of the those writers and editors are single white males who have roommates then families with kids. So to them they are just not interested in Wii Fit or Animal Crossing when they can play Halo or Gears. Mario Kart and SSBB is fun but they can play Soul Caliber IV and Wipeout HD with their buddies who are not in the industry.
Look at the cast of 1up Yours. Garnett is married but no kids who drinks heavily. Shane a single guy who I believe lives with a cat and David Ellis, another single minded guy who into sports and shooters. John is the only one on there with a family and for most part champions the good of the Wii but knows not even try to sell it as a core machine. He knows that the games are for the mainstream audience and he can see how well most of those games will fit in that lifestyle, especially through the eyes of his young sons.
Like it or not, the Wii dismissed has a lot non Nintendo core gamers this year, so those core game writers and podcasters have dimissed the Wii this year. Maybe next year...