I've noticed those too:) 

I don't mind low ratings, but it was quite funny. Comment : "excellent, fantastic!" Rating - two stars.
What I think it  is just lack of... guts, heh. People are more honest with stars thinking artist won't be able to tell who gave lower rating, so they  are 'safe' (and can tell what they really think)...

IMO it again shows one of the biggest cancers in this community. Lack of honesty,  andhypocrisy in galleries (but it was discussed so many times, so ...)