I have noticed this on a Moodle 2.0.3 and I also tried on the QA Moodle - when you go to grade an assignment, in the feedback box, you are not able to insert an image or embedded media or even make a hyperlink to a file you wish to upload - it's as if the TinyMCE editor isn't working here in the same way as it works elsewhere. I wanted to upload an mp3 file as an audio response instead of typing text but I don't get the file picker.
edit I added it to the tracker here MDL-27520 as I couldn't see it elsewhere (but I admit I still find it hard to search so I hope I haven't duplicated ) I really need this functionality