The new public diaries page has the original entry and comments listed on the same page. It also has a box to leave a comment listed below the entry or last comment left.
I think the new format provides a more streamlined process instead of having to click through multiple pages to read comments and leave your own comment.
You do have to be logged in to leave comments still. If you're reading the public diary pages without being logged in, the text box to leave your own comment will not be available.