Unfortunately, in order to give worthwhile comments on a photo you have to have some idea of what you're talking about. Most people, even photobloggers, aren't sure how to talk about photographs authoritatively. Those who are knowledgeable, probably aren't sure how well criticism will be received, so they tend to do what their mama told them and if they can't say anything nice...
It's tough, even photography sites that are supposed to specialize in critiques don't do a very good job of providing constructive feedback. The only place I've really found good feedback on my photos is from groups where I actually know the people in person and can show them prints.