I think alot of beginners that post images already know that they can, and will, improve alot on their technique. It is when an imager reaches a point where they are struggling with how to improve their images when constructive criticism can really be helpful, and quite often the imager will make it known that they are at that stage. For someone posting their first images ever it feels like an achievement for them and I don't think constructive criticism is warranted at that stage (unless directly asked for) but over time I'm sure all people that want to progress further will gladly take all constructive criticism on board as being productive. I guess it is up to the commentors to simply recognise at what stage of the learning curve the imager is at - someone who is stoked just to capture something or someone who's improvements are starting to slow down and is really posting to get feedback on how to improve their technique. I think that their is a healthy mix of both on the forums atm
