While many blogs have a basic form in which to submit your details, including your URL, more and more of them have third party blog commenting software installed. One of the best known of these systems is Disqus.
This is a good platform in a lot of ways. So you should sign up to it.
Apart from anything else it speeds up the process of commenting because you don't have to keep manually inserting your details for every new blog. You just log in and it will include the URL you've got in your profile.
Not only can it be found on a lot of blogs, but quite a few big news and magazine sites use it as well, for example The Telegraph and Rolling Stone.
Some sites like these these get absolutely huge traffic. So if you post a really good comment -- particularly if it's soon after an article is published -- you may well get a torrent of readers clicking through to your blog.
Then there's the fact that you're considerably raising the odds of having your blog seen by both mainstream journalists and editors. Get enough of them to be aware of it and you never know, you might get mentioned in the body of a subsequent post. If you get enough of this kind of exposure and take advantage of it you might even end up writing for the publication at some stage.