The change to the ability to edit comments may have been made for the same reason it was done on another photo site I help moderate. We had a few morons who would leave extremely inaccurate and rude critiques then, after other people complained about them in their own comments, would go back in and completely change their original post. That made those who complained look stupid. I don't understand the mentality of those who do that kind of thing but it was happening so regularly that we felt we had no option.
Hi everyone, I've spoken to the web team and they have told us this feature will be coming back soon. They are just upgrading a couple of our sister sites and once that's done, we'll see the new features on DP's site