The link is assumed to be marketing. We all know what it is. Hopefully the site will tell us why it is interesting or useful. But, we know it's a landing page trying to get people to sign up.

However, when you use marketing babble in a comment, it adds no value to the conversation. "Join millions of..." that is just not helpful to the HN conversation.

Now, if the comment was -- "we developed this to try and solve X problem for Y users. Let use know what you think or if you have questions..." -- then it might have been a useful place to start the conversation. Marketing copy is not.

(And they probably did more harm than good by posting that comment)