Your point is a very important one that I was surprised to find was not expressed by other commenters. It convinced me of something that was bouncing around my head while reading the article and the comments before yours:

If, as everyone seems to agree, movies are becoming more 'safe', more 'lowest common denominator' on average, reviews should be becoming _less_ polarized in response, not more.

That the opposite is happening suggests that reviews are progressively carrying less and less 'truth' than they once did, and this is likely the case even when they may be in general agreement on a given film.