People glom onto the only entity bothering to do benchmarks/reviews/ratings/whatever, or at least the only popular one, even if the system is totally bogus.
I don’t get any of this, really. MetaCritic and IMDB are also huge, and use alternate weighting systems, I believe. You can also just google the movie and underneath the ‘big three reviewers,’ there’ll be a bunch more quality review sites, like NYT, The Guardian, Ebert’s site and so forth.
So for anyone who wants to get a spectrum of opinions, it’s really not that hard. Not unlike how one should get reliable news.