The curious case of critics

The other day, film critic Rajeev Masand tweeted that there is no God if James Franco was not nominated in the Best actor category at the Oscars. In the review that followed, he raves about the movie and there is not a single negative point he has cited. And he gives it 4 out of 5 stars.
He writes:

The extraordinary cinematography by Anthony Dod Mantle and Enrique Chediak, and AR Rahman’s haunting score complement Boyle’s rich and imaginative storytelling style. And James Franco who appears in more or less every scene delivers a performance nothing short of spellbinding.

Question: Can someone please enlighten me on why he refrained from giving it 5 out of 5 if, in his opinion, the movie scores full marks in all aspects?

I have watched some reality shows on Indian television where one of the judges marks a performance 21 out of 25, while the other one marks it 23/25, without any explanation on how this score was arrived at!

The wonderful guys at the fabulous Sound Opinions, rates a record as buy it, burn it, or trash it. When I heard it the first time, I didn’t get what “burn it” meant, and on reading up:

Burn it! ...There are a few good tracks here, but not worth the full price....try a downloading service, or (cough), another method.

This is kind of, I would say, innovative and "adapting to the times".

Maybe, someday, all critics would follow a thumb rule, like Siskel and Ebert did – Up or Down? Which is it?

Gene Siskel boiled it down: "What's the first thing people ask you? Should I see this movie? They don't want a speech on the director's career. Thumbs up--yes. Thumbs down--no."

PS: I attended a session by Rajeev Masand in Bangalore in 2010 and found him to be genuine. When my brother asked him what he thinks about The Big Lebowski, he more or less admitted that he didn’t get it the first time and that he is planning to watch it again. That was an honest response!