I think you can edit the title of a topic in any section for a limited amount of time right after you create it, but I'm not sure for how long. I know i have edited titles of topics in the pictures section and the tutorials section, but right after I created them (within half an hour, anyway)
The "Update" titles you are seeing may be NEW threads, given the "UPDATE" in the title so that people would know that they revisit an old thread's topic.