There was no pre-tense that those games were ever going to be amazing review scorers. Also, they are going to sell amazing anyway so why would any Wii fan be fretting over it? Heavenly Sword was proported (by Sony fans) to save the system from it's lacklaster sales which it failed to do dispite decent reviews.
I also don't think Nintendo has gotten an easy ride, SSBB scored incredibly well because it's an incredibly balanced and polished game with a truly ridiculous amount of content. SMG, MP3 were also excellent games by any standard.
Personally, Mario Kart is a bit disappointing to me, I expected better and I don't think it deserves a better score (but it is fun). As for WiiFit - I could almost care less what video game reviewers have to say, I want to see what fitness experts have to say about it. Those are the reviews that matter.