The thing is that, for me, growing as a writer is a must. I work hard to learn new things, new tricks and styles all to become a better writer. So I tend to assume that everyone would want to become better, and I comment on their stories to that extent, because that's what I would want people to do with my stories. It tends to make me read a story with more of a critical eye than one of enjoyment. It's a bad habit. I know what a good story looks like (I may not yet be able to write one :-P)so I do a lot of comparison.