Pages submitted to HN should simply not be behind login walls, which is why I flagged this.
This thread already has multiple references to the fact that you have to log in to see the submitted post. There are many HN users without a FB account. For them, the headline of the submission cannot be verified by clicking on the link.
Although there is a large intersection between the two groups of HN and FB users, you don't have to be signed up with any other webservice in order to use HN. This is not only about FB. As a matter of principle posts to HN should be accessible for all HN users without requiring them to sign up with any other webservice.
However, this is up to PG and the HN community. It would be good if PG provided a guideline whether submissions behind login walls are accepted or not.