On my site, commenting is not enabled.
But at the top of each blog post (except for one, strangely), there's a 'Leave a reply' link.
(the link doesn't do anything -- but the words 'leave a reply' sitting there obviously make it look like you can leave a reply...)
I don't see any 'discussion module' in my edit-post page.
Here's an example page with a 'Leave a reply' link, just under the post title:
I'm on Mac Chrome -- in case it's a small browser-related bug...