Site comments - is this just reciprocal back patting?

I have reviewed a number of web pages in the SIte Comments utility and, while most of them were positive, some have been negative due to confusing language, grammar, and other problems that I perceived. I would lie to get some feedback from the community on leaving "negative" feedback. My comments have always been constructive criticism and were only made to help the owner make a better presentation of their material. There have been a couple of minor things like suggesting that they remove the default Wordpress subtitle in their heading which should be no big deal in my opinion. There have been others where the language was so stilted and hard to read I had to comment on that and the overall feedback was negative as a result. I do take into consideration that sometimes the author's native language is not English and don't criticize that too much but mildly suggest that they have their content reviewed by someone who does have a better grasp of the language.

Anyway, I guess my main question is: what is the main purpose of the Site Comments utility? Is it just to get comments on the site in order to, in theory, garner better rankings or is it a medium for helping people improve their overall presentation through constructive criticism as well? Content presentation and readability are factors in Site rankings as well after all.