If we comment on a post, and we just leave a link, without real comment, it could be called spamming. However, if the link is related to the post, I think it would be OK. It’s just like comparing our point of view with the one we comment on. But, if the link is just linked to our newly made blog, and even don’t share the same interest with the post we commenting, it’s could be called shameless plug.
Another opinion: Reasons to blog
Traffic, for newbie on blogging is one of the goal. Novice on blogging is longing for the visitor traffic indicator to rise up. They even don’t pray to a big number, just 10 a day or 50 per week is very encouraging for them. I am also think like that in my first blogging experience, and sometimes when working on new blog project.
So we can overcome this shameless commenting manner by two ways. First, as a commentator, please give your point of view, short praise is not mandatory, but try to manage your comment on 1-3 sentences. It would raise your chance to have your comment are not being erased. Don’t worry to add a link to your comment, as long as you did the above things. Notice that your name (if you logged in when commenting) is an automated link to your blog (you can set the preferences).
Second, as a blog owner, especially who don’t want receiving just-link comments, be literal to your reader. You can also set a mini guide to comment on your blog. I ever see a blogger that prohibit the reader to praise him, he did this by editing the comment form. If you think that the comments are not-for-you, you can always delete them, or perhaps you can report it as spam. The person who comment without reading the post is out there, some of them eventually will visit you. Just be bold in your commenting rules, don’t post it in regular way, use a widget or modify the commenting form, so they are ‘forced’ to read the commenting rules.