If I see a Hub that's well written or otherwise particularly impressive I'll, of course, compliment it. I would never presume to critique someone else's Hub because I just think, "Who am I to critique other people's stuff?" "Critique" is generally just another way of saying "criticize"; and unless someone asks for a critique I would never presume to criticize other people's work. I don't presume to be other people's "teacher", and I don't see HubPages as English class and me as a student.
No matter what someone writes, there will always be people who don't like it or think it could have been done some other way. That's how it goes. Hubbers can't worry about pleasing everyone or hoping everyone "gives them an 'A'".
I think it's arrogant to critique when nobody asked for a critique. Whether it's on HubPages, some other site, or in life; I'm not a big fan of people who presume to criticize everyone and everything they run into. I figure, people who know how to write well write what/how they do because it is their choice. People who aren't skilled writers may not mind not having a lot of skill (or else will look for a teacher of some sort if they want one).
This may be a little arrogant on my part, but I just think, "I don't care who likes what I write and who doesn't. I'm not looking for a writing teacher, and I'm not interested in presuming to appoint myself someone else's writing teacher."