The _Start a new topic_ input field is a link. It's supposed to take you to the Flow page with ?action=new-topic, showing a form to enter a topic and its first comment. But on a brand-new board, the href parameter to the link is blank, so clicking it just redisplays the current page. It seems in flow_block_topiclist.handlebars,
is empty if the board is brand new.
Once the board has a header or a first topic, the no-JS href is there.
Compare http://ee-flow.wmflabs.org/wiki/User_talk:EmptyUserTalkPageA and ...EmptyUserTalkPageB.
The board could be smart enough in no-JS mode to detect "I have no topics to show, so I can show an expanded new-topic form in-place."
This seems low-priority while the Flow team manually enables each Flow board, ensuring each has some content.
See also bug 72064, another bug with no-JS new topic.