Ok I *think* this is a switch roles issue related to this http://tracker.moodle.org/browse/MDL-23062 but I am not sure. As admin I made a post to the news forum and then to check that students couldn't respond to it I switched my role to student - and was able to edit or delete the post. When I logged in as an actual student, it worked fine (ie I couldn't do anything with the post)

Petr "the switch role will never be 100% accurate"
Very true. As far as I know of Moodle, the switch roles feature is there to enable a teacher to see more or less what the various parts of a Moodle course will look like to a student. The "more or less" aspect varies amongst activities and modules, sometimes it is 100% and for other activities it is near impossible to completely mimick the student role.
The only way to really test moodle as a student is to log in as a real (or dummy) student.
We can only hope that the switch roles feature of Moodle 2.x will be nearer that 100% for most activities than previous versions.
Joseph